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Audio - Pro Audio Glossary of Terms
A B C D
E F G H
I J K L
M N O P
Q R S T
U V W X
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A
A-weighting
A standard compensation used in measuring audio specifications
whereby the result is modified to account for the human ear's sensitivity
to certain frequencies. A-weighting usually returns a slightly better
result than non A-weighted measurements, but to be meaningful, comparisons
between products need to done using either one standard or the other,
but not both.
A/D Converter
An Analog to Digital Converter (ADC) is an electronic device
whose function is to convert signals from the analog domain (vocals, instruments,
and stereo sources) into digital data. The data can then be recorded and
manipulated within a computer audio workstation or stand alone digital
recorder. The converters can be either built-in or standalone. The quality
of these devices can vary substantially.
(See Jitter)
ADAT Optical
A form of data transfer developed by Alesis for use in their ADAT machines.
Using light as the carrier signal, ADAT optical is similar to TosLink
two channel formula and uses a similar connector, but is optimized to
include up to eight discreet channels of digital audio. Used today as
one of several digital transmission protocols for linking digital audio
devices.
(See Light Pipe)
AES
The Audio Engineering Society (AES) is a professional body that
sets standards for the audio community.
AES/EBU
Refers to one of the digital signal protocols used to transfer
data from one digital device to another. Usually implemented physically
using 3-pin XLR connectors and 110-ohm cabling.
AGC
Automatic Gain Control (AGC) is a circuit that automatically adjusts the
level of incoming audio so as to optimize the record level of the receiving
device. Mostly employed in low cost audio and video recorders to avoid
the complication of manual adjustment.
AIFF
Audio Interchange File Format (AIFF) is a file format for storing digital
audio data. It supports a variety of bit resolutions, sample rates and
channels of audio. The format has been embraced by the Apple platforms,
but is also widely used in professional programs that process digital
audio data.
ASIO
Audio Stream Input/Output is a cross-platform, multi-channel protocol
for audio transfer that was developed by Steinberg and is now being adapted
by many manufactures of audio/MIDI sequencing applications. It allows
various programs to communicate with different sound cards and to recognize
all of the inputs and outputs available on the sound card. The user can
then assign these I/O ports as needed for recording or playback when using
an ASIO-compatible software program.
Absorption
In acoustics, the property exhibited by certain materials to
absorb (as opposed to reflect) sound waves. Used by studio designers to
control the sound energy in a given space. Also used in reference to the
conversion of sound or radio frequency (RF) energy into heat.
Absorption Loss
In wireless microphone applications, the loss that occurs when
a transmitted signal passes through a material that absorbs a portion
of the RF energy, reducing the signal level available to the receiver.
Access Time
The time it takes from when a disc access command is issued until the
read/write head reaches the data sector requested. Access time is important
in data intensive situations like hard disk recording, multimedia playback,
and digital video applications. Lower access times are better.
Active
A circuit or device that uses transistors, integrated circuits or vacuum
tubes to perform an action on an electrical source. Typically these systems
require power to operate and are often used in amplifiers or active equalizers.
The down side to using active components is the probability that noise
and distortion will be introduced into the signal. Also refers to a type
of speaker that has integrated amplification within
the same enclosure as the speaker elements.
Active Splitter
An electronic device that consists of a Radio Frequency (RF) signal splitter,
preceded by an RF amplifier that compensates for the RF loss of the splitter.
Used to allow one antenna to feed several receivers.
Adjacent Channel Rejection
The ability of a radio receiver to reject interference from an undesired
signal on another nearby channel frequency. In wireless applications,
unless the frequency separation between the desired signal and the adjacent
signal is specified, the term is generally not of any practical significance.
Aftertouch
MIDI data that is transmitted by a digital keyboard after a key has been
struck and additional pressure is subsequently exerted on the key while
it is being held down. Most often routed to control vibrato or volume,
Aftertouch comes in two flavors, Channel (or Mono) being the most common
implementation. Polyphonic Aftertouch allows for multiple keys to transmit
individual amounts of modulation data simultaneously, but few keyboards
offer this functionality today.
(See MIDI)
Algorithm
A procedure or formula for solving a problem. In FM synthesis
the term refers to the various sound producing structures employed. Also
used in effects processors, particularly reverb, to artificially simulate
acoustic spaces and other effects.
Aliasing
In digital sampling and recording, aliasing is a digital distortion that
occurs when the program material being sampled contains frequencies higher
than one-half the selected sample rate (called the Nyquist Theorem). Most
digital recording devices have filters that remove these frequencies that
would otherwise cause aliasing to occur.
(See Nyquist Theorem)
Amperage
Also referred to as amps, amperage is a measure of electrical current.
An ampere is the unit of measure for the rate of electron or current flow
past a certain point and in a given amount of time, through an electrical
conductor.
Amplifier
An amplifier is an electronic device that increases the voltage,
current or power of a signal. Used in wireless communication, broadcasting
and in audio equipment, they can be categorized as either weak-signal
amplifiers or power amplifiers. Weak-signal amplifiers are used primarily
in wireless receivers, acoustic pickups, audio tape players and compact
disc players. Power amplifiers are used in wireless transmitters, broadcast
transmitters and for sound reinforcement.
Antenna
A conductive physical device designed to radiate RF energy from
a transmitter, or to capture RF energy for a receiver.
Antenna Diversity
A form of diversity that uses three receiving antennas. The three
signals are combined into a single composite output that is applied to
a non-diversity receiver. No longer used by any major manufacturer due
to unpredictable and generally poor performance.
Antenna Splitter
An electronic device that consists of a radio frequency signal splitter
(power divider) preceded by an RF amplifier that compensates for the RF
loss of the splitter. Used to allow one antenna to feed several receivers.
Arpeggiator
A device for electronically creating a series of notes from a
synthesizer. Rather than playing held notes simultaneously, the arpeggiator
plays the notes in series. On some synthesizers this may be a simple iteration
of the held notes in ascending or descending order, while on other synthesizers,
very complex algorithms are employed to trigger notes in seemingly random
and sometimes outrageous manners.
Attenuate
Attenuation is a general term that refers to any reduction in
the strength of a signal, whether digital or analog. It is a natural consequence
of signal transmission over long cable runs, or it may be purposely achieved
with circuits to prevent overload and distortion in an audio signal path.
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B
BNC Connector
A type of small "twist and lock" RF connector often used with
coaxial cables and antennas in wireless systems. Also used in audio and
video to carry clock signals. A BNC male connector has a pin that connects
to the primary conducting wire and then is locked in place with an outer
ring that turns into a locked position.
BPM
Abbreviation for Beat Per Minute, a standard way to define tempo,
often used in electronic music and sequencing software.
Balanced Circuit
A signal-carrying circuit that employs two conductors, each of
which carries the same signal potential but with the polarity of one reversed
with respect to the other. Any noise that is induced into the circuit
will be common to both "legs" and on arrival at the destination,
is cancelled out by combining the out of phase signals. Applies equally
to balanced lines. Balanced connectors are generally 3-pin XLR or TRS
1/4" phono.
Banana Plug
A connector that is designed primarily for connecting speaker
wire to the binding posts on the back of power amplifiers.
Band
A range of frequencies, as defined by a regulatory authority
or by commonly accepted usage. In audio, the term usually refers to equalizers,
in particular graphic EQ's. In telecommunication, a frequency band is
a specific range of frequencies in the radio spectrum. Used in wireless
microphones.
Bandpass Filter
An electronic device or circuit that allows signals between two
specific frequencies to pass, but that attenuates signals at other frequencies.
Bandpass filters that have amplifiers for boosting the levels of signals
in the accepted frequency range are known as active filters. Devices that
do not amplify and consume no power in doing their task are referred to
as passive filters.
Bandwidth
Technically the term refers to the width of the range of frequencies
that any digital or analog signal occupies on a given transmission medium.
Audio bandwidth is generally given as 20 Hz to 20kHz, although there are
harmonic components in audio that extend far above the 20k point. Generally,
when presented as a specification, the wider the frequency response the
better. However, in practice this can be misleading, since there is no
uniform method or point in a signal chain that manufacturers must adhere
to when making this measurement.
Bantam
Used to describe patch bays or cables based on the Western Electric/AT&T
long frame switchboard. Sometimes referred to as TT bays. Liked by professional
installations because of the large number of points that are available
for a given size patch bay.
Bargraph
A display device indicating a value, usually by means of a row
of LED's or LCD segments. One or more LED's or LCD segments illuminate
to display the present value of the function being monitored. Bargraphs
have replaced fragile and expensive mechanical meters for most low-cost
audio equipment.
Barrier Strip
Also know as a terminal strip. A series of screw terminals arranged in
a line, to which other devices are connected. Popular on equipment from
about twenty years ago due its low cost and reliability, nowadays the
connectors are mostly found on amplifiers or crossovers that are going
to be installed into permanent installations.
Bias Voltage
A low DC voltage typically supplied by a body-pack wireless transmitter
to power a condenser microphone. Not to be confused with phantom power.
Binding Post
Type of output connector on a power amplifier, or as the connector
on a speaker cabinet. A very versatile connector, accepting banana plugs,
alligator clips, and bare wire. Usually color-coded.
Bit Depth
In digital audio, the term is used to define the number of bits
a digital device uses to process audio. While sampling frequency determines
the outer frequency limits that a piece of hardware is capable of processing,
bit depth refers to the dynamic range that can be captured during recording.
The number of possible "levels" that can be recorded at 16-bit
is 65,536, while this figure jumps to 16,777,216 using 24-bit hardware.
The human ear is very sensitive to these levels, and given properly implemented
converter designs, 24-bit recordings will sound more "open"
than 16-bit recordings. However, it is also true that a top of the line
16-bit converter could sound better than a very poorly implemented 24-bit
converter. Although bits and sampling frequencies are important specifications,
the kinds of filters used, and the integrity of the audio path prior to
the converters is also very important as to how a particular converter
will sound.
(See Floating Point)
Black Burst
Also referred to as house or video sync. Derived from video editing
where video decks and cameras needed to proceed from one frame to other
with absolute synchronization, the term is now finding use amongst audio
professionals as they find the need for their digital workstations to
lock to picture when working on film or video projects. A black burst
generator simply outputs a video signal with no picture content. All the
equipment that need synchronization is connected to this generator, and
since they are all receiving the same clock signal, they remain locked
to each other. Not to be confused with SMPTE time code, which is used
for positional reference.
(See Clock, SMPTE Time Code)
Boundary Microphone
A type of microphone that detects sound pressure level changes
at a boundary of the acoustic space in order to reduce interference between
direct and reflected sound.
Breathing
Generally an unwanted side effect of using compressors in an
incorrect manner, whereby the background noise of the source material
rises and falls depending on the behavior of the main program. Also referred
to as pumping.
Brickwall Filter
A type of filter in which the cut-off slope is very steep, almost
resembling a wall. Sometimes used in converters to remove source material
above the Nyquist frequency, but the negative results of phasing and attenuation
of bands near the center frequency make them unusable for higher end applications.
Broadcast Wave File
A subset of the standard .wav audio file format commonly used
by PC's. The specification restricts what kind of audio data can be carried,
along with extra data that provides information on the title, date, time
etc. of the audio file. It's most important function for digital audio
is the provision for time stamping which allows users to move individual
files from program to program and have the ability to "spot"
the file to it's original position.
Bulk Dump/Load
A feature of MIDI devices that allows the transfer of specific
data between devices. Bulk dump/load was of ten used to back up MIDI data
via System Exclusive messages, and is still used for that purpose today
by lower cost hardware.
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C
Cable Loss
The inherent loss of coaxial RF cables due to conductor resistances, absorptive
losses in the insulating material and signal leakage between the braids
of the outer shield.
Capsule
The portion of a microphone that converts acoustic energy to
electrical energy. Often includes shock mounts, acoustic isolators, protective
covers and electronic circuitry in addition to the basic transducer. Also
called an element.
Cardioid
A microphones pickup characteristic, notably strong sensitivity
to material presented to the front of the microphone, while sensitivity
falls off from sources arriving at an angle of 90° or greater away
from the front, and good rejection from the rear. The name derives from
a representation of the polar pattern, which loosely resembles a heart
shape. Prone to exhibit pronounced proximity effect, where bass frequencies
are accentuated the closer the source to the microphone.
(See Hypercardioid)
Carrier
A modulated RF signal. That is, one which is carrying audio or
other information. FM and AM radio employ two carrier signals but modify
them in different ways. FM synthesis uses a carrier as part of the algorithm
for generating sound. The carrier usually outputs the original sound source
and is subsequently modified by other operators to change the timbre and
other characteristics of the sound.
Center Frequency
The particular frequency to which a given filter-band in an equalizer
is tuned to. Parametric equalizers are able to sweep the center frequency,
providing a greater degree of flexibility to the EQ, while graphic EQ's
have a number of fixed center frequencies. The amount of boost/cut that
can be applied to the center frequency will also affect adjacent bands
to a greater or lesser degree, based on the "width" or Q that
is set on the filter.
Channel
In wireless, a designated radio frequency available for use by the transmitter
and receiver. In audio, the circuit path for a signal, or a functional
unit that is designed to independently process a signal.
Circumaural
Used in reference to headphones and means "around the ear."
Can be combined with semi open, closed and open back designs.
(See Supra-Aural)
Clipping
Clipping occurs in analog and digital audio circuits when the incoming
signal exceeds what a particular device can accommodate. Visually, it
results in the flattening of the signal peaks, as if the waveform had
been "clipped" off. In certain analog circuits light clipping
can have a positive effect, producing a pleasing distortion. In digital
circuits the general rule is that clipping is to be avoided at all costs,
since it produces a nasty and harsh sound.
Class A
A type of amplifier design where the output device is always
on for both parts of a complete sinusoidal cycle. Class A is the most
inefficient of all power amplifier designs, averaging only around 20%.
Because of this, class A amplifiers are large, heavy and run very hot,
due to the amplifier constantly operating at full power. The positive
effect is that class A designs are inherently the most linear, producing
the least amount of distortion and are thus often found in high-end audio
equipment.
Class B
Class B is opposite to class A in that the current in a specific output
flows for one half cycle. In other words, both output devices are never
on simultaneously. This system allows for much better efficiency, but
displays poor linearity around the crossover region, since it takes time
to turn one device off and the other device on. This in turn translates
into extreme crossover distortion, thus restricting class B designs to
power consumption critical (battery operated) applications, such as two-way
radio and other communications audio.
Class AB
A class AB amplifier is a combination of both class A and B in
that the output bias is set so that current flows in a specific output
device appreciably more than a half cycle but less than the entire cycle.
That is, only a small amount of current is allowed to flow through both
devices, unlike the complete load current of class A designs, but enough
to keep each device operating so they respond instantly to input voltage
demands. Thus the non-linearity of class B designs is eliminated, without
the inefficiencies of the class A design.
Class H
If an amplifier has more than one voltage rail then it is designated Class
H. Its operation involves changing the power supply voltage from a lower
level to a higher level when larger output swings are required. For most
musical program material the output stage is connected to the lower supply
voltage, and automatically switches to the higher rails for large signal
peaks. If fact the input signal actually modulates the higher supply voltage.
This allows the power supply to track the audio input and provide just
enough voltage for optimum operation of the output devices. Using multiple
power supplies improves efficiency enough to allow significantly more
power for a given size and weight.
Clock
In digital audio or video, a clock serves as a timing source.
Data has to be executed at very specific times for digital audio or video
to function properly. An issue that has to be addressed when synchronizing
systems with each other. Although audio and video require different references
to keep data passing through a system correctly, they both do it with
the aid of a clock. This could be black burst, word clock, or clock embedded
in a digital data stream, such as AES/EBU or S/PDIF.
(See Black Burst)
Clock Speed
In a computer, clock speed refers to the number of pulses generated
by an oscillator that sets the tempo for the processor. The faster the
processor can access data, the faster the computer can perform its functions,
given that other parts of the system are sufficiently tuned to support
the particular clock speed. Clock speed is determined by a quartz-crystal
circuit, similar to that used in radio communication equipment, and is
measured in megahertz (MHz)or even gigahertz (GHz.)
Closed Back
In reference to headphones, describes the design of the cup where
there is no venting of the audio to the outside. Closed back, circumaural
headphone are often used in studios, where "bleed" from the
headphone can be picked up by the recording microphone. Closed back headphones
minimize this problem.
Coaxial Cable
Called coaxial because the cable includes one physical channel
that carries the signal, surrounded by another concentric channel, both
running along the same axis, but separated by insulation. They are used
for high frequency transmission of telephone, television and audio signals.
Coaxial cable was invented in 1929 and first used commercially in 1941.
For audio, different types of cabling are required for analog as opposed
to digital transmission.
Compression
The function accomplished with an audio compressor. A circuit
is employed to reduce gain by a variable amount when the output begins
to exceed the preset threshold. In wireless microphones, the process of
reducing the dynamic range of the audio signal by a factor of 2:1 via
a logarithmic compressor for transmission.
Compressor
A circuit that performs compression of an audio signal. By setting
the ratio and threshold controls, the user is able to tame large dynamic
swings. For instance, a 2:1 ratio means that if the program material rises
by two decibels, the output will only rise by one decibel, once the threshold
setting has been exceeded. There are many uses for compressor, from controlling
the large dynamics of live performances, increasing the overall level
of a signal, increasing the sustain on a guitar or just evening out a
performance. Other controls such as attack and release times will further
modify the source material.
(See Limiter)
Condenser Microphone
Type of microphone in which the capsule consists of conductive
diaphragm next to a backplate. The entire assembly is given an electric
charge, (often via phantom power) which basically creates a capacitor
out of the capsule. Sound waves hitting the diaphragm cause it to move
in relation to the backplate, producing a variation in the capacitance
of the capsule. This in turn produces a variance in the output voltage,
which can then be turned back into acoustic energy.
(See Electret Condenser Microphone, Phantom Power)
Confidence Monitoring
Listening directly from the recording medium while recording
is in progress, thus ensuring the source material is being recorded correctly.
Used in high-end analog recorders and DAT machines, a secondary head reads
the recorded material immediately behind the record head. This allows
the user to monitor the actual recording to detect any errors, and therefore
one can say that the recording is done with full confidence.
Contact Microphone
A contact microphone receives its entire signal from being in
contact with a particular surface and the resulting mechanical vibrations,
not from airborne sound waves. Sometimes referred to as piezo or transducer
microphones.
Control Surface
Available in many sizes and levels of complexity, control surfaces
are used to control the functions of some other device, often a computer
software program. Particularly in computer based audio recording and mixing,
a control surface can replace the tiresome use of the computer mouse,
and provides a physical connection with many or all of the parameters
in a given piece of software. Additionally some control surfaces can provide
additional features that are usually found on dedicated consoles, such
as talkback facilities.
CoreAudio
Refers to the built-in audio capabilities of the Mac OS X. Similar
to Sound Manager found in earlier Apple OS, CoreAudio deals with the way
audio is handled within the computer and any application that is written
specifically written to support it. Two of the major advantages that CoreAudio
has over Sound Manager are support for multi-channel audio and the ability
to specify exact outputs on connected hardware, and the inclusion of high
sample and bit rates. Although still in its early days, Apple's move to
provide these features as part of the OS will speed the rise of "native"
applications, and perhaps bring a seismic shift to computer audio production.
CoreMIDI
Similar to CoreAudio, the term refers to the built-in MIDI support
embedded in Apple's OS X.
Crossover
An electrical device that divides the audio spectrum of a particular
source into smaller groups of frequencies, making it easier for down stream
components to handle the load. The most common use of crossovers is in
amplifier/speaker systems, which allows the separate components to function
more efficiently. For instance, a mid-range speaker will function better
if it does not have to deal with low frequency content, and visa versa.
Crystal
In wireless microphones and digital devices, a frequency stabilizing
device consisting of a small quartz crystal in a holder. The quartz naturally
vibrates and the frequency can be made highly stable by external circuitry.
This in turn is used to establish the operating frequency of wireless
transmitters, receivers and other RF and digital equipment.
Crystal Controlled
In wireless, equipment whose operating frequency is directly
established by a crystal, rather than indirectly as in a frequency synthesizer.
Also commonly used to refer to equipment that is only able to operate
on one fixed frequency, as versus a number of synthesized frequencies.
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D
DAE
Digidesign Audio Engine is the underlying code that allows Digidesign
software communicate with computer platforms and operating systems. DAE
is required for third party software to access Digidesign hardware. Prior
to HD systems, DAE was an actual separate application. For HD systems,
DAE is now integrated into the Pro Tools application.
DAT
Digital Audio Tape. A two track 16-bit digital recording and
playback system.
DAW
Digital Audio Workstation. Usually refers to a computer with
audio recording, playback and editing features. Nowadays, entire projects
can be completed on DAW.
D/A Converter
Digital to Analog converter. The opposite of an A/D converter
where audio signals in the form of digital data are reconstructed back
into an analog waveform. As with ADCs, DACs come in a variety of configurations
and prices ranges, and vary in how faithfully the program material is
reassembled.
(See Jitter)
dB
The decibel (abbreviated dB) is a unit used to measure the intensity
of a sound. However, the dB scale is not linear, rather it is a unit used
to express the relative levels of two electrical voltages, powers or sounds.
It is never an absolute value.
dBu
Also sometimes referred to as dBv, it is dB referenced to voltage.
0dB equals 0.775 volts.
dBV
dBV also references voltage, but does so without regard for impedance.
0dB equals 1 volt. The dBV rating is most commonly found in reference
to consumer equipment that uses operating levels of -10 dBV.
DC Offset
An imbalance that can sometimes occur at an A/D converter, where
DC (direct current) which is basically a constant voltage, is introduced
into the digitized signal. Apart from reducing headroom, DC content can
introduce clicks and pops while the audio is being edited.
DVD-R
A recordable DVD disc. Not to be confused with DVD-RAM and DVD-RW,
both of which are rewritable mediums. DVD-R is a write once, read many
medium which currently holds about 4.7 gigabytes of information.
DVD-RAM
A type of DVD media that is designed for storage and backup. No other
equipment other than the drive itself is required for a user to use DVD-RAM.
In fact, DVD-RAM discs act very much like hard drives, other than being
a much slower medium, in that a user can simple drag and drop files on
to the desktop icon.
Damping Factor
In reference to power amplifiers, the damping specification is
the ability of the amplifier to control speaker motion once signal has
stopped. The effects of damping are most apparent at low frequencies -
an amplifier with a high damping factor will make a speaker sound "tighter"
in the low end, while low damping factors result in indistinct bass.
De-Esser
Device for reducing the effect of sibilance in vocal signals.
Basically, a de-esser is a frequency dependent compressor, although these
days such devices are very sophisticated and optimized in the way they
tackle the problem of sibilance.
Detent
Physical click stop in a control knob/switch such as a pan or EQ cut/boost
knob.
Diaphragm
The portion of a microphone that is mechanically moved by sound
waves. The resulting interaction with a backplate or moving coil (depending
on the microphone type) allows the conversion of sound energy to electrical
energy. This energy eventually gets to a loudspeaker or headphone, where
a roughly equivalent reverse process takes place as the cone moves in
response to the electrical signal and produces sound energy.
Dipole
A type of antenna with two defined opposing radiating elements,
both of the proper length for the frequency of operation, and each forming
a counterpoise for the other.
Direct Box
Often abbreviated as DI (short for Direct Inject) used primarily
as a device for matching the impedance of a source to the inputs of a
tape machine or mixer. Typically, the output of a bass or electric guitar
is a high impedance, unbalanced signal, that needs to be converted into
a low impedance balanced signal, either for long cable runs to a live
console, or for imputing into a recording device. The process also allows
the electronics on these instruments to function at their correct levels,
thus often improving the sound.
Directivity
The property of transmitting /receiving energy more strongly
from/to certain directions, than others.
Disc-At-Once
A method of "burning" a CD, disc-at-once writes to
the disc in one pass - the laser in the CD burner never turns off, even
in silent passages. Required by mass duplicators of Red Book audio CDs.
Although CDs written track-at-once will generally play in consumer CD
players, the duplicators at mass manufacturers will reject such a disc
as fatally flawed.
Distortion
A term that has taken on a specific meaning, but which is in
fact much broader in its definition. Technically, distortion is any change
in the shape of an audio waveform compared between two points in a signal
chain. Therefore adding EQ and compression also adds distortion to the
original signal. But generally the term refers to the desirable or undesirable
"breaking-up" of audio (as in distorted guitars.)
Diversity
A method of reception providing protection from signal loss due
to multi-path nulls, which are localized small areas with a very low RF
signal level caused by multi-path propagation.
Downsample
The taking of a audio file with a high sample rate, and sample
rate converting down to a lower sample rate. Used in particular when a
project is recorded at a high sample rate and the audio files need to
be prepared for CD distribution.
Dropout
In wireless microphones, a loss of RF signal, which in turn results
in loss of audio or audio that is noticeably noisy. Also refers to a small
physical area where there is insufficient RF signal present to obtain
satisfactory wireless operation. Dropouts are normally caused by multi-path
or signal blockage due to some type of obstruction. Also refers to areas
on oxide tape where there is a problem with the coating and where subsequently
audio or digital data is not properly reproduced.
Driver
Piece of software that handles communications between the main
program and a hardware peripheral, such as a soundcard, printer or scanner.
Drivers are constantly being updated due to OS rewrites and the like.
D-Sub
Refers to a type of multi-pin connector that is commonly used for computer
connectivity, although in last few years manufactures such as Tascam and
Digidesign use the D-Subminiature connector for supplying multi-channel
audio to and from their systems.
Ducking
A system for controlling the level of one audio signal with another. For
example, background music can be made to "duck" whenever there
is the need to hear a voice over.
Dynamic Microphone
A type of microphone that consists of a diaphragm connected to
a coil that operates in a magnetic field. Any movement of the diaphragm
due to sound pressure levels moves the coil within the magnet, thus producing
an electric current. Dynamic microphones do not require external power
to operate, are generally more robust, and therefore favored for live
use (although several manufactures are making condenser microphones specifically
for live use.) The downside is that due to their construction, dynamic
microphones are less sensitive to fast transients and don't have the high
frequency response of the condenser variety.
Dynamic Range
The range in dB between the noise floor of a device and its defined
maximum output level. The term applies to both audio devices and RF equipment.
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E
EASI
Acronym for Enhanced Audio Streaming Interface developed by Emagic,
and is designed to standardize communication between audio software and
hardware. The standard is cross-platform and is similar to ASIO, developed
by Steinberg, but differs from ASIO in that Emagic has made EASI totally
public, with no need to sign non-disclosure agreements.
EIN
EIN is a specification that is mostly relevant to microphones
and preamplifiers. It stands for Equivalent Input Noise and deals with
the self noise that is a feature of virtually every piece of electronics.
Since microphones output a low-level signal, any noise present will be
boosted proportionately. The specification is usually measured with a
200ohm source resistance, which on its own produces a level of noise that
when referenced to a line level signal is equal to -129.6dBu of noise.
This is theoretically the lowest noise level that can be obtained, but
some manufactures play with this figure a little by measuring their equipment
with lower source impedance.
Early Reflections
The initial sound reflections from walls, floor and ceiling,
created when an acoustic event happens in an acoustically reflective environment.
Often a parameter that can be adjusted in units that electronically simulate
acoustic spaces (reverb processors.)
Electret Condenser Microphone
As the name implies, a variation on a condenser microphone, but
with a permanently charged plate in the capsule. This negates having to
supply external power to the microphone.
(See Condenser Microphone)
Emission
In wireless microphones, the radiation of an RF signal, whether
intentional or not.
Enhancer
Originally design to add back some of the high-frequency content
lost in audio production due to multiple passes using analog tape. Techniques
used include dynamic equalization, phase shifting and harmonic generation.
Envelope Generator
All sounds can be described in a variety of ways. One of them
is the manner in which a sound evolves amplitude-wise, starting from silence
to full volume to final decay. Or how the harmonic content changes over
time. In synthesizers, these changes to an oscillator or filter are achieved
using envelope generators. EG have various break points supplied to help
adjust the rates and levels of the various parts of the envelope.
Equalizer
Hardware device or computer plug-in used to alter the frequency
balance of an audio source. An equalizer has the ability to boost or cut
specific frequency ranges based around a center frequency and can be used
either creatively, to drastically alter a source, or in a corrective manner,
such as in a mastering situation, to even out anomalies in a mix. Equalizers
come in various forms, including parametric and graphic, active or passive.
(See Filter, Graphic, Parametric)
Expander Module
Synthesizer with no keyboard, often rack mountable or in some
other compact form. Useful for users who already have a keyboard and do
want another one, but want the sounds offered.
Expansion
In wireless microphones, the process of restoring the original
dynamic range of the audio signal by means of a 1:2 logarithmic expander.
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F
FET
Field-Effect Transistor typically used as an impedance converter
at the element in a condenser microphone. A MOSFET is a particular kind
of FET, which is finding itself used more and more in power amplifiers.
(See MOSFET)
Feedback
In acoustics, the undesirable leakage of audio from loudspeakers,
back into the same microphone which is being used for originally capturing
the audio. If too much feedback occurs, the system can go into self-oscillation,
causing unpleasant howling or squealing. In electronics, such as power
amplifiers, feedback can be used to achieve specific results, such as
performing input/output comparisons.
Feedback Eliminator
An automatic electronic device that senses the onset of feedback,
and cancels it before it gets out of hand. This is achieved by using a
specialized equalizer with multiple, very narrow filter bands, positioned
between the audio source and the speakers. The unit "searches"
for the beginnings of feedback, analyzes the problem frequency and cuts
that band. Good eliminators carry out this whole process in mere milliseconds,
and can respond to the fact that feedback may occur at many different
frequencies throughout a live performance.
Figure-8
A microphone polar pattern whereby the capsule is most sensitive
to sound sources from the front and back equally, but sounds from the
sides of the microphone are rejected. Sometime referred to as bi-directional.
Also describes certain antenna patterns, such as that of a dipole.
Filter
An electronic circuit designed to attenuate a sound source's
energy at a particular frequency. A true filter is always passive, in
that it does nothing to add to the signal. However, most filters these
days have amplifiers attached to them to allow the user to both boost
and cut particular frequencies (active filters.) Multiple filters can
be combined to create equalizers that are either passive, active or both.
(See Equalizer)
FireWire
Apple computer's version of the IEEE 1394 standard, which is
a high-speed data exchange protocol. FireWire provides a single plug-and-socket
connection on which up to 63 devices can be hung. Additionally, the technology
allows for hot-swapping devices, while data transfer allows for speeds
of up to 400 Megabits per second. Common on personal computers these days,
FireWire is also finding its way into consumer electronics, particularly
digital video.
(See IEEE-1394)
Flanging
Flanging is an audio process where two copies of the same signal
are played together, with one variably delayed against the other. Originally
created using two tape machines and "leaning" gently on the
flange of one of the tape reels, today the effect is produced using digital
effect processors. Feeding the processed signal back into the device to
be processed again can deliver a more intense effect, although many are
of the opinion that the original tape based method is still superior.
Floating Point
A data encoding process that allows the representation of very
large numbers with fewer bits. Used in computers that have floating point
registers, and where complex graphics, scientific or audio processes need
to be executed rapidly. As far as audio is concerned, a debate is presently
centered around whether floating point or fixed-point computation is better
for the end product, in terms of sonics. So far there does not seem to
be a consensus on this issue, since there are advantages and disadvantages
to both systems.
(See Bit Depth)
FM Synthesis
Originally developed by John Chowning of Stanford University,
and later popularized by Yamaha's FM7 synthesizer, FM synthesis is a method
of sound generation where a sine wave is modulated by one or more sine
waves to produced a large variety of waveforms. Later incarnations of
the process used many other types of waveforms for the carrier and modulators,
producing an even wider palette of sounds. Know primarily for the pure
bell-like and electronic piano tones
Formant
An emphasized frequency component of an instrumental or vocal
sound that does not change with pitch, and which helps to distinguishes
one instrument from another, and gives voices their unique characteristic.
Problems arise in the audio world where pitch shifting is common, (samplers,
DAW editing) since in this case the formant characteristic is pitch-shifted
along with the overall pitch of the signal, making the resulting audio
file sound unnatural. Various manufactures of pitch shifting processors
have tried to address this issue with a modicum of success.
Fragmentation
The process by which data written to a hard drive is stored in
small packets that may or may not be next to each other. The result of
continual erasing and saving from/to the hard drive, severe fragmentation
can cause a slowdown in drive performance with drive intensive applications
like digital audio, since the head mechanism has to constantly jump around
to read all the data.
Frequency
In audio the indication of how many cycles of a repetitive waveform
occurs during one second. A waveform which repeats once per each second
has a frequency of 1Hz (Hertz.) Frequency also references to human hearing
as pitch.
Frequency Response
A measurement of the frequency range that can be handled by a
specific piece of electrical equipment or loudspeaker when referenced
to amplitude. A graph of all the frequencies plotted versus level is the
Frequency Response Curve of a particular piece of equipment.
Frequency Stability
In wireless applications, the accuracy to which the operating
frequency is maintained over time and in the presence of environmental
changes.
Frequency Synthesizer
A circuit to generate a stable and precise RF output on any one
of a number of preset (or programmable) frequencies. Synthesizers are
used as the local oscillators for receivers, and to set the output frequency
of transmitters.
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G
GS
An extension to the General MIDI protocol developed by Roland
for use in its own synthesizers.
Gain
The extent to which a circuit amplifies a signal. Usually part of an amplifier
specification, its value is most often expressed in a decibel value.
Gain Before Feedback
The amount of total gain that can be achieved in an audio system,
from microphone to speakers, before the onset of acoustic feedback.
Gate
A dynamic device that has the ability to stop audio passing through
it based on a certain threshold. Originally designed to shut down audio
output in passages with no program material (where tape hiss might be
evident) or to lower bleed on drum microphones. Gates can also been used
creatively, notably the gated reverb of Phil Collins' 80s drum sound.
General MIDI
An addition to the original MIDI specification that allows for
consistent playback on any instrument that is GM compatible. Achieved
by requiring that groups of sounds have very specific locations (a piano
sound on one synthesizer will have the same location on another,) that
all instruments have 24-voice polyphony, and that certain continuous controllers
are similarly defined. In theory, music sequenced for General MIDI should
play back on any other GM instruments with the similar type of sound on
the same MIDI track with any volume and pan information also being executed
as written.
(See MIDI)
Gooseneck
A flexible metal coupling that is used to attach a microphone
to a stand or podium. Used mostly in conferencing and for podium mounting,
the metal spiral allows the microphone to be adjusted into a multitude
of positions.
Graphic Equalizer
The term nowadays refers to a type of equalizer where 15 or more, narrow
frequency bands are controlled using sliders, either boosting or cutting
the individual bands. The term graphic came about because the arrangement
of the sliders provides a visual representation of the EQ curve. Graphic
equalizers can still be found that use rotary controls instead of faders.
Ground Effect
The loss of operating distance due to the positioning of wireless
antennas too close to the ground. Reflected RF energy from the ground
gets mixed in with the direct RF signal and causes cancellation of RF
energy at the antenna. In certain situations the loss can be significant.
UHF systems are less susceptible to this effect than are systems that
use VHF, due to the shorter wavelength of the former.
Ground Lift Switch
A switch found on some equipment that disconnects the shield
of a balanced cable from the local equipment ground. Used in situations
where ground loops are problem.
Ground Loop
A condition where current circulates in the ground wiring system, due
either to the grounds at the end of a length of cable being at different
AC potential, or where a video or audio system has multiple paths to ground.
Manifests itself usually by varying levels of hum (in audio systems) or
as rolling bars in the picture of a video system. One way to deal with
it is to use ground lift switches, but generally it is better to find
the offending piece of equipment and then checking it to find out why
it is causing the ground hum.
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H
Hammer Action
In search of the ultimate "piano-feel keyboard" synthesizer
manufacturers have often employed weights on the back-end of individual
keys to simulate the action of real pianos. However, to really achieve
a similar feel, certain manufacturers have resorted to installing hammers
on the end of the keys, which when the key is struck, moves the hammer
to strike a surface. The resulting feel is much closer to that of a piano's
actual playing action.
Handheld Transmitter
A wireless microphone transmitter consisting of both the microphone
and the transmitter electronics in one integrated package.
Handling Noise
Refers to the sensitivity that a microphone exhibits to movement,
the actual holding of the microphone and shock. A microphone's ability
to lower handling noise is a direct result of the construction of the
microphone, and to that end, some manufactures employ internal shock mounts
for the capsules to eliminate as much handling noise as possible.
Hard Disc
A high capacity computer storage device that is based on a rotating rigid
disk with a magnetic coating onto which data may be recorded. The hard
disc drive should technically refer only to the mechanism that controls
the positioning, reading, and writing of the hard disc, but today hard
disc, disc drive etc. are terms that are commonly used for the combination
of the two parts.
(See IDE, SCSI, Seek Time)
Harmonic
A harmonic is a wave whose frequency bears a whole number relationship
to the frequency of a reference signal. Complex sounds, such as the human
voice or the sound of a stringed instrument always consist of a fundamental
frequency and then a number of harmonics, which, depending on their amplitude,
will make up the basic characteristic of that sound. So the second harmonic
is always two times the fundamental, and so on through the rest of the
harmonic series. Discordant sounds have several or many harmonic waveforms
that do not bear the whole integer relationship present in the basic sound.
Harmonic Distortion
The result of passing audio through some electronic device. Since
it is impossible to make a perfectly linear device (audio out exactly
matches audio in) harmonic distortion is always a byproduct of signal
processing. The amount of distortion a particular piece of electronics
creates is in most cases kept as low as possible, particularly in reference
to "transparent" microphone preamplifiers. However, sometimes
the "coloring" is acceptable and indeed favored, and can be
taken to extremes.
Headroom
The difference expressed in dB between the nominal operating
level of a device, and the maximum level that can pass through the device
without being distorted.
Headworn Microphone
A small microphone mounted on a short boom and held in place
close to the performer's mouth by a headband or similar device. Used by
performers who need their hands free during dance numbers or to play an
instrument.
Helical Antenna
A type of antenna formed by a coiled small-diameter spring, usually covered
in plastic and somewhat flexible. Physically shorter than a standard 1/4-wavelength
whip antenna, but also considerably less efficient.
Hertz
A unit of frequency, named after Heinrich Hertz, a 19th century
German physicist. So if a complete single cycle of a waveform occurs over
1 second, the waveform is said to have a frequency of 1Hz.
High Pass Filter
A filter that attenuates frequencies below a certain cutoff point,
while passing on frequencies above the cutoff unaffected. Sometimes referred
to as low-cut filter.
(See Filter)
Host Based
Used in reference to computer based recording systems. In the
early days of computer recording, much of the processing work had to be
done on additional hardware cards, while the computer merely provided
visual feedback. But because of the unprecedented power that is available
in today's computers, it is entirely possible to have a virtual studio
within the computer, using only the computers processing power. Host based
systems are still hampered to some degree when compared to their hardware
card equivalents, but as computer power increases, so host based systems
become more and more economical.
HRS Connector
A type of audio connector often used for the microphone connections
on wireless body-pack transmitters. The connector wiring is not standardized
within the wireless industry. Also referred to as a Hirose Connector
Hypercardioid
A type of microphone pick-up pattern. Similar in shape to a cardioid
pattern, except that the sides have the greatest amount of rejection,
as opposed to a cardioid pattern where the rear of the microphone has
the least sensitivity.
(See Cardioid)
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I
IDE
Integrated Drive Electronics is a standard electronic interface
that is used as a data path for a computer's disc storage devices. IDE
drives are cheaper and less expensive to implement when compared with
SCSI drives. And whereas SCSI drives have traditionally been viewed as
more robust and quicker than the IDE counterparts, the gap between them
is shrinking due to the general reliability of hard drives in general.
Apple suspended the use of the SCSI interface in their computers several
years ago, and now provides the cheaper EIDE bus, which is an enhanced
version of IDE.
(See SCSI)
IEEE-1394
A high-speed data exchange protocol, it provides a single plug-and-socket
connection on which up to 63 devices can be hung. Additionally, the technology
allows for hot-swapping devices, while data transfer allows for speeds
of up to 400 Megabits per second. Common on personal computers these days,
IEEE 1394 is implemented by Apple as FireWire, and by Sony as iLINK.
(See Firewire)
IF
Intermediate Frequency. Wireless receivers normally convert the incoming
RF signal to a lower intermediate frequency for amplification and final
filtering prior to demodulation.
I/O
Abbreviation for input/output. In audio, the term refers to the
physical inputs/outputs of a particular piece of equipment. Also used
to describe any operation, program or device that transfers data to and
from a computer.
Image Frequency
In receivers, the process of converting the desired RF frequency results
in an undesired sensitivity at a second RF frequency, which is referred
to as the image frequency. RF filtering in the receiver is relied upon
to reduce to acceptable levels the receiver's susceptibility to spurious
RF signals at the image frequency.
Image Rejection
The measure of a receiver's ability to reject signals at its
image frequency. Normally expressed as the ratio, in dB, of the receiver's
sensitivity at the desired frequency versus the sensitivity at the image
frequency.
Impedance
An expression of the opposition that an electronic component,
circuit or system offers to AC or DC current. Impedance contains both
resistive and reactive components, although generally only the resistive
part of the circuit is usually quote in specifications as Ohms. So the
higher the resistance, the higher the impedance.
Initialize
To restore a piece of equipment to its factory default settings.
Insert Point
A connector at a particular point of a circuit that allows for
the introduction of a piece of external equipment, so that the original
signal now flows and is processed by the external equipment prior to being
returned back into the original circuit.
Intercept Point
A measure of the inter-modulation performance of a RF devices.
Devices with high intercept points will generate lower levels of undesirable
inter-modulation products as compared to similar devices with lower intercept
points.
Interface
A device that acts as an intermediary to two or more pieces of
equipment. An audio interface for a computer allows signals generated
by a preamplifier for example, to be communicated to the computer software.
The software itself is also an interface, but in this instance it is between
the operator and the computer itself.
Inter-modulation
A process that can result in distortion. Inter-modulation is
the result of two or more frequencies inter-reacting with themselves and
generating new frequencies that are not present in the original signal.
These are invariably based on the sum and difference of the original frequencies.
Isochronous
The process in IT (information technology) that requires near
exact timing coordination to successfully transmit information, such as
video or audio data. Isochronous data transfer ensures that data flows
continuously and at a steady rate so that the receiving mechanism can
display the result without interruption.
Isotropic
An isotropic radiator is a transducer that produces useful electromagnetic
field output in all directions with equal intensity, and at 100% efficiency.
In wireless applications the isotropic radiator is theoretical, although
the dipole antenna roughly approximates it. It is used as a standard reference
source against which the performance of other antennas is measured.
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J
Jam Sync
Jam Sync is a setting that is selectable when using a synchronization
device with SMPTE time code. It allows the receiving synchronizer to regenerate
time code if there are errors or drop outs in the original code. If jam
sync is not used, then a drop out will cause the slave device to go off
line.
(See SMPTE Time Code)
Jitter
Jitter is the deviation of some aspect of the pulses in a digital
signal. In audio applications, Analog to Digital converters are one of
the most critical components that are susceptible to jitter. Using an
internal or external clock, an A/D converter "slices" an incoming
audio signal into a number of pulses that digitally conforms to the original
source. These pulses have to occur and proceed with very strict timing,
and any periodic displacement of the signal from its ideal location will
cause jitter. Jitter can be caused by the converter having a poor clock,
or when source impedance is incorrectly matched at the load. The results
are heard as low level distortion or noise, and since high frequencies
are more susceptible to jitter, a loss of high end definition. The issue
is that once jitter has been introduced into the digital data it is impossible
to remove it.
(See A/D Converter, D/A Converter)
Jog Wheel
A physical controller that allows a tape machine's transport
to move tape back and forth a small distance to find an edit point. Originally
used by video editors to find an exact location on tape, jog wheels can
be found on audio control surfaces to provide similar functionality within
a digital audio editor.
Joystick
Gamers have traditionally used joysticks for controlling games.
It is a device that allows control of two different axes simultaneously.
Certain synthesizer manufacturers have utilized the principle instead
of using separate modulation and pitch wheels, but the main usage of the
device is now beginning to appear in surround sound production. Pan pots
are two- dimensional devices (left/right,) and since surround sound requires
at least four points to define an audio source location (left/right/front
and left/right/rear,) joysticks are a common feature on surround consoles
and control surfaces.
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K
kHz
The kilohertz is a unit of alternating current or electromagnetic
wave frequency equal to one thousand hertz. The unit is used in measurements
of bandwidth, but in audio can also refer to the pitch of a particular
tone.
Keymap
Term is used in reference to a synthesizer or sampler that uses
sample data for the raw building blocks of the sound generation. It is
a means to assign each sample to a particular key or range of keys. So
a piano keymap would theoretically have each tone from the entire piano
keyboard mapped to exactly the same keys on the synthesizer or sampler.
A second keymap might contain similar information, except that each note
was sampled using a stronger/lighter strike of the piano keys. Of course,
it is not always necessary to assign one sample per key. In fact one could
assign a single sample across the entire keymap. Different manufactures
refer to keymaps by other names, such as Key Group or multi-sample.
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L
LCD
Liquid Crystal Display. A technology used for displays in notebook and
other small computers, all the way to advanced VGA computer screens. It
is also found on lower cost electronic music devices. LCD's are generally
manufactured utilizing a single crystal plate and a specific pattern of
electrodes. Applying voltage between the electrodes changes the phase
of the light travelling through, or reflected by the material, thus altering
the information displayed.
LED
Light Emitting Diode. A semiconductor device that emits light
when an electric current passes through it. Used for status lights or
bar graph meters in many audio devices, LED's are also found everywhere
from watches to laser disc players. Some LED's emit infra red energy and
are found in remote control devices and wireless headphone systems.
LFO
Low Frequency Oscillator. An oscillator that is designed primarily
to operate below the threshold of human hearing (though not exclusively)
and to provide modulation function. Often found in synthesizers and effect
devices. For instance, vibrato, a cyclic variation of pitch is generated
by modulating the audible portion of the signal with an LFO which, depending
on its pitch of the LFO, will create a slower or faster vibrato.
Latency
Latency is an issue that can be found in several areas of audio
production. In its broadest sense it means the delay that increases response
time beyond the time desired. For instance, in a MIDI keyboard instrument,
there is a slight delay, or latency, between when a key is struck and
when the actual sound is produced. In computer based recording systems
that use native processing, a delay exists between an audio event being
imputed, and when the same event arrives at the monitoring stage. The
delay will increase if the computer has to deal with any real-time processing.
To avoid the discomfort that is experienced by this delay, many systems
employ input-only monitoring during overdubbing.
Lavalier Microphone
A type of miniature microphone that is usually worn fastened
to clothing or hung around the neck. Designed for situations where a microphone
would be obtrusive, such as film sets or TV talk shows, the microphone
is typically made with a steep high pass filter to reduce noise generated
from the microphone moving against clothing. Also know as a clip-on or
lapel microphone.
Light Pipe
An optical cable. The term was originally coined by Alesis to
differentiate between their 8-channel protocol and the 2-channel optical
connectors found on CD players and DAT recorders. The actual fiber optic
cable used is the same in both cases, only the form of the transmission
is different.
(See ADAT Optical)
Limiter
Similar in principle to a compressor, a limiter is an audio processor
that prevents the amplitude of an audio signal from rising above a certain
threshold, regardless of what is happening to the amplitude of the source
audio. Dynamics below the threshold are more or less unaffected. Certain
compressors can in fact function as limiters if their ratio can be set
to infinity:1. Uses for limiters include maximizing levels for CD release,
optimizing recording levels for imputing into a DAW or when going to tape,
or to protect users of in-ear monitors from sudden volume surges.
(See Compressor)
Line Level
Although the term refers to the average level of a signal, these
days use of the term is more specific and applies to the two line level
references, balanced and unbalanced. Balanced or professional equipment
operates at +4dBm or 1.23 volts, while unbalanced or semi-professional
equipment operates at -10dBV or 0.32 volts. Although the distinction between
professional and semi professional equipment is blurring, the important
fact is that the two levels should not be speaking to each over. If two
pieces of equipment need to be connected that use different line levels,
then matching transformers need to be used. Otherwise the +4dBm signal
will overdrive an -10dBV input and equally a -10dBV signal will not deliver
enough level to a +4dBm input.
Linkwitz-Riley
Seigfried Linkwitz, a Hewlett Packard engineer along with a co-worker
Russ Riley, authored a paper in 1976, in which they described a new form
of crossover, which improved vastly on the standard that existed at the
time. Nowadays, many crossover designs in the sound reinforcement community
utilize the Linkwitz-Riley filters.
(See Filter)
Local On/Off
A function of an electronic keyboard, that allows the use of
the keyboard and the sound generating section to be used independently
of each other. Using a MIDI router, it is possible to control the sounds
of remote devices without triggering additional sounds from the sound
source of the triggering synthesizer.
(See MIDI)
Lowpass Filter
A filter that attenuates frequencies above a certain cutoff point,
while passing on frequencies below the cutoff unaffected. Sometimes referred
to as high-cut filter.
(See Filter)
Low Impedance
A loosely defined audio term used to describe devices whose input
or output impedance is less than approximately 5,000 Ohms. For microphones,
Lo-Z commonly is 50 - 1,000 Ohms.
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M
MAS
MOTU Audio System is a plug-in engine developed by Mark of the Unicorn
for use in its software. Plug-in engines developed by competing manufacturers
do not support MAS. However, by using an extension called VST Wrapper,
Performer is able to utilize VST plug-ins.
MDM
Modular Digital Multitrack. A digital recorder that can be used
in conjunction with other similar format machines to provide a greater
number of tracks than a single machine. Originally pioneered by Alesis
with the ADAT format and Tascam with their DA series, machines that conform
to these standards can be synchronized in a more transparent manner with
up to 128 tracks acting like a single machine.
MIDI
Musical Instrument Digital Interface. Originally developed in
the early 1980s to control one digital synthesizer from another, today
MIDI is used to transmit almost every aspect of a musical performance.
However, it must be understood that MIDI data is all about how a sound
will be produced, not the actual sound itself. So data sent from one device
to another could find itself being played with a piano sound while the
original information was actually a drum sequence. General MIDI was in
part introduced to alleviate this problem, except that the subset was
really a consumer format and of not much use to the professional community.
Amongst the command sets of MIDI are note-on, note-off, key velocity and
pitch, modulation such as pitch bend, program changes, timing and many
more. Its use has moved outside of strictly music and is used for lighting
cues amongst other applications. The one great advantage of MIDI, apart
from its ubiquity, is that file sizes are relatively small compared to
what an actual audio file would be. The MIDI protocol uses eight-bit serial
transmission with one start bit and one stop bit, has a 31.25 KBPS data
rate, and is asynchronous. Connection is made through a five-pin DIN plug,
of which only three of the pins are generally used.
(See General MIDI)
MIDI Interface/Patch Bay
A means of distributing multiple independent MIDI streams usually
based around a sequencing station. The original MIDI specification allowed
for 16 discreet channels of information to flow through a single cable.
With the arrival of multi-timbral synthesizers, a single stream of MIDI
information could easily be dedicated to a single synthesizer, and any
other units connected to the same source would also be forced to play
the same information. By connecting a MIDI interface to a computer, most
sequencing software is able to create multiple MIDI streams, each with
16 discreet channels of information that can then be routed to multiple
sound sources. Along with MIDI patch bays, which are generally free standing,
these devices are often capable of more than just distributing the MIDI
streams, including the ability to filter messages, transpose certain channels
and lots more.
MIDI Sync
Synchronization systems available to MIDI users that include
MIDI Clock and MIDI Time Code.
MIDI Thru
A MIDI connector found on electronic synthesizers, that passes
through untouched the MIDI data that is received by the MIDI input.
MIDI Time Code
A form of time code that is based around real time. Like SMPTE
time code, the units of measure are hours, minutes, seconds, frames and
subframes, but sent as part of the MIDI stream.
(See SMPTE Time Code)
MIDI Time Stamping
A term coined by MOTU to denote a method of coding MIDI data
to allow the computer to re-trigger this information with grater accuracy.
Before time stamping, MIDI transmission suffered from a certain amount
of "slop" due to a sequencer program having to rely on the host
computer's clock to manage timing issue. But with the advent of USB MIDI
interfaces and time stamping, this is no longer an issue.
MOSFET
The MOSFET is a particular type of Field-Effect Transistor (FET)
where the output current flowing between the source and drain terminals
is controlled by a variable electric field applied to the gate terminal.
The gate design determines the type of FET. In the MOSFET, the gate is
insulated from the channel by a very thin (typically less than the wavelength
of light) layer of glass. This means the MOSFET has practically infinite
impedance, which makes it useful for power amplifiers. They can also be
found in some integrated circuits (IC) and often used in wireless microphone
receivers.
(See FET)
MP3
MPEG-1 Audio Layer 3 is a standard established by the Moving
Picture Experts Group for compressing audio files. Using perceptual coding,
file sizes are reduced by a factor of 12, without too much damage to the
sound quality of the original file. Indeed, some argue that because of
the way data is discarded, there is no perceptible difference in sound
quality between an MP3 and the original sound file. However, most audio
professional would disagree. The format is used extensively throughout
the Internet, both legally for demonstration purposes, and of course illegally,
as in the recent Napster controversy.
Mic Level
The level of a signal generated by a microphone. Generally ranging
between 0.001 to 0.005 volts, to make it useful for recording, the signal
requires a microphone preamplifier to bring the signal up to line level.
Midrange
Often refers to the middle part of the audio frequency spectrum,
as perceived by humans. For example, a midrange driver would be a speaker
that was optimized for that particular range.
MiniDisc
A format introduced several years ago by Sony that allows recording and
playback of audio to and from a small magneto optical disc with a capacity
of 140MB. To be able to record 74 minutes of music, the technology applies
a data compression algorithm called ATRAC that compresses the data by
about 5:1, but also permanently changes the file on decompression. Therefore
it is know as "lossy" algorithm. However, the advantages are
a very compact size, a claim of 1,000,000 reuses of the media and the
ability to random access data on the disc.
Mini-plug
A miniature phone plug, available in both mono and stereo versions.
The most common size for audio use is 3.5 mm (1/8".)
Mini-XLR Connector
A Switchcraft Tini-QG connector, frequently called a mini-XLR,
is available in several configurations. The connector is often used on
small boundary microphones, and for the microphone connections on some
wireless body-pack transmitters. The pins are numbered in the opposite
direction from a standard XLR but the wiring scheme is not standardized
within the microphone industry.
Mixer
A device for summing two or more electrical signals. In general
audio usage, a device to process and sum the outputs of two or more microphones
or line level sources
Modulation
Modulation is the addition of a control signal to an electronic
or optical signal carrier. In electronic synthesis, one example might
be the sine wave output of a low frequency generator (LFO) being added
to a pitched note produces vibrato. Another form of synthesis uses the
principle of frequency modulation (FM) to generate a whole range of sounds,
by modulating the frequency of an audible frequency with the frequency
of another signal. AM and FM radio both employ modulation to broadcast
their signals.
Monitor
In audio applications, the term is synonymous with a reference
loudspeaker that is used for recording and mixing. They come in various
shapes, sizes, configurations and can be passive (requiring an amplifier)
or powered (built-in amplifiers.)
Mono Bridge
A feature provided on two channel power amplifiers that allows
the two channels to be combined to produced a single channel output to
a speaker than would otherwise be possible from either channel alone.
Usually engaged by a dedicated switch.
Moving Fader Automation
A type of mixing automation that uses small motors to control
the physical faders, which may or may not be used in addition to VCA.
On high priced consoles and control surfaces these are generally touch
sensitive, requiring only the placement of a fingertip on the fader to
commence updating the automation information. The advantage of moving
faders is that the fader is always at it's correct position at any given
moment, thus giving visual feedback to the engineer of each channel's
status. Additionally, many engineers prefer the use of faders without
the additional use of VCA's since in their opinion, the inclusion of these
components can degrade audio quality.
Multichannel
In wireless microphones, generally refers to a transmitter or
receiver that has more than one user-selectable operating frequency.
Multicoupler
An electronic device that consists of a RF signal splitter preceded
by a RF amplifier that compensates for the inherent RF loss of the splitter.
Allows for feeding several receivers from one antenna.
Multipath
Radio frequency signals arriving at a location via different
transmission paths, usually from a combination of direct and reflected
signals. The direct and reflected signals are often opposite in phase,
which can result in a significant signal loss. The problem is most apparent
indoors and in areas where many metallic surfaces are present.
Multipath Null
A small area or space where direct and reflected RF signals from
a transmitter cancel each other, resulting in little or no usable energy
being available to a receiver antenna.
Multi-pattern
Refers to a type of microphone where the polar pattern of the
capsule can be changed, either using a switch a changing out the capsule.
Multitimbral
An electronic synthesizer or sampler that is capable of playing
back multiple parts simultaneously, each under the control of a different
MIDI channel. Not to be confused with polyphony, which refers to total
number of simultaneous notes (or voices) that is available to the whole
instrument.
(See MIDI)
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N
Native
In reference to digital audio and computers, the term means software
that uses the processing power of the computer, and does not require additional
hardware. Also sometimes referred to as host based. However, plug-in architectures
that are written for native systems are not technically native themselves,
since they require the presence of other software to actually function.
Near Field
Although not technically correct, the term near field is generally
applied to a loudspeaker system that is designed to be close to the monitoring
position. In this way the listener receives more of the direct sound from
the speakers, while minimizing the effect of sound produced by reflections
from walls, floors and ceilings.
Neodymium
A rare-earth metal element that can be made into magnets, amongst
other things. However, it is its properties for making stronger magnets
than other materials of the same size that make the element of interest
to the audio community. Used in microphones, it can produce greater output
than non neodymium versions, for headphones it allows for lighter drivers
and for speaker design it allows for more powerful drivers for a given
size.
NiCad
The Nickel Cadmium is a type of rechargeable battery that is
used in electronic equipment. Although they have an even power discharge,
they provide less operating time than corresponding alkaline batteries.
Noise Floor
The amount of self-noise generated by a piece of electrical equipment
when it is at rest (no signal passing through.) All such devices generate
noise to some extent or another, and engineers are constantly striving
to lower this artifact. Measured in decibels.
Noise Reduction
A range of technique developed for reducing the amount of noise
in an audio signal. Dolby NR is an example of a system designed to reduce
the amount of tape noise that is inherent in the analog tape medium.
Noise Shaping
A system developed to compensate for the quantization errors
that are introduced into digital audio files when reducing the bit rate
of the data, such as when preparing audio for CD duplication. A certain
amount of noise is added to the audio data, which helps to smooth the
errors. In which part of the audio spectrum this noise resides varies
from one developer to another.
Noise Squelch
A squelch detection technique that monitors noise at the FM demodulator
output, at frequencies above the audio range. A high level of noise in
this region indicates a weak or unusable RF signal, or some form of interference.
(See Squelch)
Non-diversity
A standard single-channel RF receiver.
Nyquist Theorem
A principle used by engineers when designing equipment for the
digitization of analog signals. Due to the complex nature of sampling
audio, the theory states that for any given sample rate, the maximum bandwidth
of the analog source must fall below one half the sampling frequency.
If this formula is not followed, errors in the form of aliasing will be
introduced into the data file. To prevent this happening, analog to digital
converter usually have steep filters to remove any material above the
Nyquist frequency.
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O
OS X
Apple Computers latest incarnation of their operating system,
described as being the first complete revision. Apart from the fact that
Apple maintains that the OS will make future revisions easier, for audio
two features stand out. Memory protection that prevents a "crashed"
application from bring down the whole computer, and the addition of core
audio, where functions of audio production that were previously taken
care of by applications are now part of the operating system.
Off-Axis
Term used to describe the position of a sound source in reference
to the microphone recording the source. Generally, a microphone will record
best when the source is directly in front of it, but since moving the
microphone off-axis results in coloration of the signal, engineers sometimes
use it to good effect.
Off-line
Although used to describe the temporary condition of not being
connected to a network, for audio and video purposes the term refers to
the processing of files that is not done in real time. Often it is because
the computational device is not fast enough to perform the operation while
the source is playing. In postproduction, the act of non-linear editing
is also considered off-line.
Ohm
Unit of electrical resistance. Named after its founder Georg
Ohm, Ohms law states that current varies in direct ratio to the wires'
resistance.
Omnidirectional
Describes a device such as a microphone or antenna that operates
equally well in all directions.
Open Reel
A type of tape recorder that uses tape that is wound on spools
rather than inside a casing, such as a cassette or DAT tape
Optical Compressor
A type of audio processor where a light source is used as a means
of controlling the amount of attenuation applied to the audio signal.
A form of compression developed in the late 50's and while found mostly
in high-end equipment, reissues of "vintage" opto compressors
have seen a resurgence lately.
Orange Book
The name for Philips and Sony's recordable CD standard published
in 1990. In addition to specifying the first recordable CD formats, the
specification also deals with how the data is managed, hybrid disc and
multisession operation amongst other things. With the publication of the
Orange Book specification, users were able for the first time to perform
desk top disc writing, a function taken for granted today.
(See Red Book)
Oscillator
An electronic circuit designed to generate a period electrical
waveform at a particular frequency. Oscillators are found in computers,
wireless receivers and transmitters, and music synthesizers. Early synthesizers
used oscillators as the raw source for creating sound, using filters and
envelops to shape the sounds.
Overload
A condition where the signal levels present exceed the capabilities
of a device, causing an undesirable consequence, such as distortion.
Oversampling
Used during analog to digital and digital to analog conversion
and refers to the process whereby the converters sample at much higher
rates than the base frequency. This allows the filters to be much gentler
in slope, which results in less phase distortion in the audible spectrum.
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P
PCI
Peripheral Component Interconnect, originally designed by Intel,
is an interconnect system for sending data between the CPU and peripherals
independently of the processor. Found on many desktop computers these
days, not only those based around Intel processors, the standard allows
for 32-bit transmission of up to 132Mb per second, and has found a use
in such high data rate applications as digital audio and video. 64-bit
PCI busses are also now available.
PCMCIA
Personal Computer Memory Card International Association was organized
in 1989 to promote standards for credit card-size devices that can fit
in a portable computer. Originally designed as a storage device, it later
expanded to other applications such as modems and networking. For audio
and video users, the technology has been extended to include input/output
devices. PCMCIA cards come in the same rectangular size, but differ in
thickness according to application.
POW-r
Psychoacoustically Optimized Wordlength reduction is a sonically
transparent digital word length reduction algorithm, reducing 20, 24,
and even 32-bits files to the CD standard 16-bit format. Pow-r is technically
not noise shaping, although it performs a similar function, and aims to
retaining a high degree of perceived dynamic efficiency with very low
noise. The algorithm is scalable, meaning it is ready for all sample rates,
even to 192kHz and beyond.
PPM
Peak Program Meter. A type of meter designed to register signal
peaks rather than the average level of an electrical source.
PPQN
Pulses per Quarter Note refers to the timing resolution of a
MIDI sequencer. It refers to the number of subdivisions within a quarter
note that a MIDI event could possibly start on. Nowadays resolutions are
high enough (960 ppqn and more) that most sequencers will accurately reproduce
what is played into them, compared to early sequencers that had resolutions
of 96 ppqn, and sounded mechanical.
(See MIDI)
PZM
Pressure Zone Microphone. Also know as a boundary microphone.
The microphone consists of electret capsule mounted to a backing plate,
which is then placed on any kind of flat surface. Useful for conferences,
ambient microphones or for recording piano where isolation from other
sources is essential.
Pad
An electronic circuit that attenuates the output of a particular
device. Often found on microphones, pads are used to bring down the microphone's
output level for use with a preamplifier that would otherwise become overloaded
due to a hot input.
Pan
To pan, or panning refers to the act of moving the perceived
location of a sound source within a stereo soundstage. Generally works
by reducing or making louder the particular sound source in either the
left or right channel of a stereo output. Although slightly more sophisticated
electronics are used to control this movement accurately, the net result
is the same. If a source is panned hard left, then it will appear at only
the left speaker, and likewise with the right side. The amounts of signal
present in both speakers will determine the exact location of the sound
source in between the left and right sides in the stereo field.
Parametric Equalizer
An equalizer whose filters contain controls over three parameters.
Frequency and gain/cut are obvious, but the third parameter is a little
more complex, and refers to a measure of the sharpness of the resonant
peak. In other words, with a narrow Q, gain or cut affects fewer frequencies
adjoining the center frequency, while a wide Q will affect a greater number
of adjoining frequencies. Expressed as a ratio, a higher Q factor indicates
a narrower bandwidth, while a lower number indicates a wider response.
Thus, assuming a constant center frequency, Q is inversely proportional
to bandwidth.
(See Filter, Quasi-Parametric, Q)
Passive
An electronic device that does not use any amplification circuits.
Applied mostly to filters, it describes a cut-only design, and because
of this, passive circuits are less prone to distortion. In practice, even
though a filter is described as passive, it may none the less have make-up
gain circuitry at its output to compensate for the loss in power that
cutting can cause.
Passive Radiator
An element in speaker design that is used to improve the bass
response of smaller cabinets. Consisting of a diaphragm that resembles
a woofer, but without the voice coil, it is meant to move sympathetically
with the energy delivered by the active woofer. While providing a greater
bass response, the diaphragm is hard to control and can lead to overtly
boomy bass response.
Patch
Also called a program, a patch refers to a single programmed
sound on a synthesizer or sampler that can be recalled by a program change
command. Also refers to a temporary fix for software that is publicly
released, in which a bug was not previously found during the testing cycle.
The patch is usually incorporated in the next software revision.
Patch Bay
A patch bay or patch panel is a means of bringing together the
cabling from various pieces of equipment to a central location, thus simplifying
interconnection. Developed from the days when operators manually connected
two telephone callers by inserting a patch cord between two sources, patch
bays today can be a little more sophisticated, allowing for more than
just connecting one piece of equipment to another.
Peak
Maximum instantaneous level of a signal, peak is the maximum value, either
positive or negative that a waveform achieves. Important in audio in that
when a signal peaks beyond what a circuit can handle, distortion appears.
Peak Hold
The part of a non-mechanical meter, where the topmost LED will
stay lit to indicate an over. Useful in digital recording or mastering
situations where any overs are undesirable. Often the length of time a
meter will display the over is user definable as is what constitutes an
over (how many successive samples.)
Phantom Channel
A feature in surround systems that allows for the creation of
center channel information when a center speaker is not part of the set-up.
Achieved by folding what would be center information into the left and
right speakers. This produces a "phantom" center image.
Phantom Power
DC voltage, usually 48V that is supplied to a condenser microphone
using the signal cores of a balanced microphone cable. Condenser microphone
need a source of power to function and nowadays most consoles and preamplifiers
provide this feature.
(See Condenser Microphone)
Phase
Waveforms are repetitious. That is, they proceed through regular
cycles. Phase is defined as to how far along a cycle the waveform is,
with 360 degrees being the point of a completed cycle. Most engineers
take phase into account while capturing an audio source with multiple
microphones, since audio hitting different microphones even with a small
delay, can put the summed audio out of phase, which results in certain
frequencies of the original sound source being attenuated or even cancelled.
In fact, if a waveform is combined with an exact copy of itself but with
the two being 180 degrees out of phase, they will cancel each other out
completely.
Phase Lock Loop
A phase locked loop (PLL) is an electronic circuit that has a voltage
driven oscillator that is constantly adjusted to match the frequency of
an input signal. Operates by comparing the phase of a sample signal, usually
the frequency-divided output of the RF oscillator, with a precision fixed
reference frequency. The compared phase output then drives a control loop,
which forces the RF oscillator frequency to be an exact multiple of the
reference frequency. Used in audio for providing low jitter clocks for
WC generators and in certain analog to digital converters.
(See Jitter)
Phone Plug
A 1/4" connector found on a lot of audio equipment. The name derives
from the old telephone switchboards, which used 1/4" patching cables.
Generally available in two varieties, unbalanced or TS, and balanced or
TRS, where T stands for tip, R for ring and S for sleeve.
Phono Plug
A type of connector originally used by RCA to connect their turntables
to amplifiers. The name has stuck, and these kinds of connectors, found
on consumer and semi-professional equipment are today still referred to
as RCA phono connectors.
Physical Modeling
A type of synthesis that utilizes computer modeling to analyze
and then describe how the physical properties of an instrument affect
its tone production. This information can then be written into an algorithm
that mimics the output of such an instrument.
(See Algorithm)
Piezo
Derived from a Greek word that means to press, for the purposes
of audio, Piezo microphones are manufactured by coupling a diaphragm to
a small layer of crystal. When vibration causes the diaphragm to vibrate
and therefore "push" against the crystal, a shift of electrons
occurs within the crystal, thus creating a potential difference. Piezo
microphones are sensitive to the source of the vibration, but insensitive
to the outside world, and are useful as contact microphones or triggers
for electronic drums.
Pigtail
Description of an audio cable that has bare ends rather than
a specific type of connector. Often found on wireless microphone applications.
Pilot Tone
A specific tone frequency outside the human audio range, applied
to a transmitter. Used by tone coded squelch systems for receiver squelch
control.
Pitch Bend
A control message within the MIDI specification that changes
the pitch of a synthesizer in response to the movement of a lever or pitch
bend wheel.
Plug-In An application that runs within a parent application and adds
functionality. In digital audio, plug-ins have become ubiquitous, with
several manufactures providing standards for developers to write plug-ins
for various platforms. These include TDM, VST, DirectX, Audiosuite and
MAS and cover functions as diverse as reverb, dynamics, time based effects,
EQ, limiting, dither, guitar amplifier emulation, virtual synthesizers
and more.
(See MIDI)
Polar Pattern
A polar pattern is a plot of a device's sensitivity as a function
of the angle around the device. Used to define the characters of microphones
and antennas, the plot of the polar pattern will show how well a device
will reject sounds from a certain angle (the back of a microphone) or
from which angle it is most sensitive.
Polyphonic
The ability of an instrument to play more than one note simultaneously.
Technically, a piano is 88 note polyphonic, although if the human element
were to be taken into consideration, then it would take 8.8 people to
fully exploit all 88 notes simultaneous. Likewise, a six-string guitar
has a maximum polyphony of six notes. However the term is mostly applied
to digital synthesizers to specify the maximum number of voices that are
available to the entire instrument. Because synthesizers are often multitimbral,
not all voices need to be assigned to a single sound. In the early days
of synthesis, voice allocation was often fixed or needed to be user specified.
These days voicing is generally allocated in a dynamic manner.
Pop Filter
A means of shielding microphone capsules from explosive burst
of air from a performer's mouth. Made from an acoustically transparent
material, pop filters can either be built into the surrounding mesh of
the microphone itself, or more commonly made from material stretched across
a separate circular form, and attached to a microphone stand close to
the microphone.
Preamplifier
An electronic device used to amplify low-level signals. Commonly
used to bring microphone outputs up to levels that subsequent equipment
can utilize.
Pre-emphasis
A system for applying high frequency boost to a sound before
processing so as to reduce the effect of noise. In FM radio systems, noise
increases rapidly in the higher audio range. To offset this, the audio
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