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ADC:
See analog-to-digital converter.
A/D converter:
See analog-to-digital converter.
ADPCM:
Adaptive delta pulse code modulation. An audio compression algorithm for digital audio
based on describing level differences between adjacent samples.
ADSR:
Attack/decay/sustain/release, the four segments of a common type of synthesizer envelope.
The controls for these four parameters determine the duration (or in the case of sustain, the height)
of the segments of the envelope. See envelope.
aftertouch:
A type of control data generated by pressing down on one or more keys on a
synthesizer keyboard after they have reached and are resting on the keybed. See channel pressure,
poly pressure.
AIFF:
Audio interchange file format. A common Macintosh audio file format. It can be mono or
stereo, at sampling rates up to 48kHz. AIFF files are QuickTime compatible.
algorithm:
A set of procedures designed to accomplish something. In the case of computer
software, the procedures may appear to the user as a configuration of software components -- for
example, an arrangement of operators in a Yamaha DX-series synthesizer -- or as an element (such
as a reverb algorithm) that performs specific operations on the signal.
algorithmic composition:
A type of composition in which the large outlines of the piece, or the
procedures to be used in generating it, are determined by the human composer while some of the
details, such as notes or rhythms, are created by a computer program using algorithmic processes.
aliasing:
Undesired frequencies that are produced when harmonic components within the audio
signal being sampled by a digital recording device or generated within a digital sound source lie
above the Nyquist frequency. Aliasing differs from some other types of noise in that its pitch
changes radically when the pitch of the intended sound changes. See Nyquist frequency.
all-notes-off:
A MIDI command, recognized by some but not all synthesizers and sound
modules, that causes any notes that are currently sounding to be shut off. The panic button on a
synth or sequencer usually transmits all-notes-off messages on all 16 MIDI channels.
amplitude:
The amount of a signal. Amplitude is measured by determining the amount of
fluctuation in air pressure (of a sound), voltage (of an electrical signal), or numerical data (in a
digital application). When the signal is in the audio range, amplitude is perceived as loudness.
analog:
Capable of exhibiting continuous fluctuations. In an analog audio system, fluctuations in
voltage correspond in a one-to-one fashion with (that is, are analogous to) the fluctuations in air
pressure at the audio input or output. In an analog synthesizer, such parameters as oscillator pitch
and LFO speed are typically controlled by analog control voltages rather than by digital data, and the
audio signal is also an analog voltage. Compare with digital.
analog-to-digital (A/D) converter (ADC):
A device that changes the continuous fluctuations
in voltage from an analog device (such as a microphone) into digital information that can be stored
or processed in a sampler, digital signal processor, or digital recording device.
attack:
The first part of the sound of a note. In a synthesizer envelope, the attack segment is the
segment during which the envelope rises from its initial value (usually zero) to the attack level (often
the maximum level for the envelope) at a rate determined by the attack time parameter.
attenuator:
A potentiometer (pot) that is used to lower the amplitude of the signal passing through
it. The amplitude can usually be set to any value between full (no attenuation) and zero (infinite
attenuation). Pots can be either rotary or linear (sliders), and can be either hardware or "virtual
sliders" on a computer screen.
auto-correct:
See quantization.
bandwidth:
The available "opening" through which information can pass. In audio, the
bandwidth of a device is the portion of the frequency spectrum that it can handle without significant
degradation. In digital communications, the bandwidth is the amount of data that can be transmitted
in a given period of time.
bank:
(1) A set of patches. (2) Any related set of items, e.g., a filter bank (a set of filters that work
together to process a single signal).
baud rate:
Informally, the number of bits of computer information transmitted per second. MIDI
transmissions have a baud rate of 31,250 (31.25 kilobaud), while modems typically have a much
lower rate of 2,400, 9,600, or 14,400 baud.
bend:
To change pitch in a continuous sliding manner, usually using a pitch-bend wheel or lever.
See pitch-bend.
bit:
The smallest possible unit of digital information, numerically either a 1 or a 0. Digital audio is
encoded in words that are usually eight, 12, or 16 bits long (the bit resolution). Each added bit
represents a theoretical improvement of about 6dB in the signal-to-noise ratio.
bpm:
Beats per minute. The usual measurement of tempo.
brick-wall filter:
A lowpass filter at the input of an analog-to-digital converter, used to prevent
frequencies above the Nyquist limit from being encoded by the converter. See Nyquist frequency,
aliasing.
buffer:
An area of memory, used for recording or editing data before it is stored in a more
permanent form.
bulk dump:
See data dump.
byte:
A group of eight bits. (MIDI bytes consist of ten bits because each byte includes a start bit
and a stop bit, with eight bits in the middle to convey information.)
card:
(1) A plug-in memory device. RAM cards, which require an internal battery, can be used for
storing user data, while ROM cards, which have no battery, can only be used for reading the data
recorded on them by the manufacturer. (2) A circuit board that plugs into a slot in a computer.
carrier:
A signal that is being modulated by some other signal, as in FM synthesis.
CD-ROM:
Compact disc read-only memory. A compact disc format that can store data other than
just standard CD audio. Many programs, sound sample libraries, and graphics are distributed on
CD-ROM because each CD can store hundreds of megabytes of information, yet costs about the
same to manufacture as a floppy disk, which only stores about 1 megabyte. See ROM.
cent:
The smallest conventional unit of pitch deviation. One hundred cents equal one half-step.
channel:
An electrical signal path. In analog audio (such as a mixer), each channel consists of
separate wired components. In the digital domain, channels may share wiring, and are kept separate
through logical operations. MIDI provides definitions for 16 channels, which transmit not audio
signals but digital control signals for triggering synthesizers and other devices.
channel pressure:
A type of MIDI control message that is applied equally to all of the notes on a
given channel; the opposite of poly pressure, in which each MIDI note has its own pressure value.
Also called aftertouch, channel pressure is generated on keyboard instruments by pressing down on
a key or keys while holding them down. See aftertouch, poly pressure.
chorusing:
A type of signal processing. In chorusing, a time-delayed or detuned copy of a signal
is mixed with the original signal. The mixing process changes the relative strengths and phase
relationships of the overtones to create a fatter, more animated sound. The simplest way to achieve
chorusing is to detune one synthesizer oscillator from another to produce a slow beating between
them.
clangorous:
Containing partials that are not part of the natural harmonic series. Clangorous tones
often sound bell-like.
clock:
Any of several types of timing control devices, or the periodic signals that they generate. A
sequencer's internal clock is always set to some number of pulses per quarter-note (ppq), and this
setting is one of the main factors that determine how precisely the sequencer can record
time-dependent information. The actual clock speed is usually determined by the beats-per-minute
setting. See ppq, bpm, MIDI clock.
clock resolution:
The precision (measured in ppq) with which a sequencer can encode time-based
information.
companding:
A type of signal processing in which the signal is compressed on input and
expanded back to its original form on output. Digital companding allows a device to achieve a
greater apparent dynamic range with fewer bits per sample word.
compression:
(1) The process of reducing the amplitude range of an audio signal by reducing the
peaks and bringing up the low levels. (2) The process of reducing a data file in size, often by noting
patterns in the data and summarizing them. Some types of audio data compression are "lossy,"
meaning the quality of the audio is reduced.
continuous controller:
A type of MIDI channel message that allows control changes to be made
in notes that are currently sounding. See controller.
controller:
(1) Any device -- for example, a keyboard, wind synth controller, or pitch-bend lever
-- capable of producing a change in some aspect of a sound by altering the action of some other
device. (2) Any of the defined MIDI data types used for controlling the ongoing quality of a
sustaining tone. Strictly speaking, MIDI continuous controllers are numbered from 0 to 122; in
many synthesizers, the controller data category is more loosely defined to include pitch-bend and
aftertouch data.
crossfade looping:
A sample-editing feature found in many samplers and most sample-editing
software, in which some portion of the data at the beginning of a loop is mixed with some portion
of the data at the end of the same loop, so as to produce a smoother transition between the end and
the beginning when the loop plays.
cross-switching:
A velocity threshold effect in a synthesizer in which one sound is triggered at
low velocities and another at high velocities, with an abrupt transition between the two. If the
transition is smooth rather than abrupt, the effect is called crossfading rather than cross-switching.
Cross-switching can also be initiated from a footswitch, LFO, or some other controller. Also called
velocity switching.
cutoff frequency:
The point in the frequency spectrum beyond which a synthesizer's filter
attenuates the audio signal being sent through it.
DAC:
See digital-to-analog converter.
data dump:
A packet of memory contents being transmitted from place to place (usually in the
form of MIDI system-exclusive data) or stored to a RAM card.
daughterboard:
A small circuit board that can be attached to a larger one (the motherboard),
giving it new capabilities. For example, some companies manufacture daughterboards that add
sampled sounds to soundcards that previously could only synthesize sounds via FM.
dB:
See decibel.
decay:
The second of the four segments of a typical ADSR envelope. The decay control
determines the amount of time it takes for the envelope to fall from the peak reached at the end of the
attack segment to the sustain level. See ADSR.
decibel:
A unit of measurement used to indicate audio power level. Technically, a decibel is a
logarithmic ratio of two numbers, which means that there is no such thing as a dB measurement of a
single signal. In order to measure a signal in dB, you need to know what level it is referenced to.
Commonly used reference levels are indicated by such symbols as dBm, dBV, and dBu.
delay:
(1) The first stage of a five-stage DADSR envelope, which delays the beginning of the
envelope's attack segment. (2) A control function that allows one of the elements in a layered sound
to start later than another element. (3) A signal processor, used for flanging, doubling, and echo,
that holds its input for some period of time before passing it to the output, or the algorithm within a
signal processor that creates delay.
detune:
Noun:
A control that allows one oscillator to sound a slightly different pitch than another.
Verb:
To change the pitch of one oscillator relative to another, producing a fuller sound.
digital:
Using computer-type binary arithmetic operations. Digital music equipment uses
microprocessors to store, retrieve, and manipulate information about sound in the form of numbers,
and typically divides potentially continuous fluctuations in value (such as amplitude or pitch) into
discrete quantized steps. Compare with analog.
digital-to-analog converter (DAC):
A device that changes the sample words put out by a
digital audio device into analog fluctuations in voltage that can be sent to a mixer or amplifier. All
digital synthesizers, samplers, and effects devices have DACs (rhymes with fax) at their outputs to
create audio signals.
download:
To transfer a file from another computer into your own. Often done by modem. See
modem.
dry:
Consisting entirely of the original, unprocessed sound. The output of an effects device is
100% dry when only the input signal is being heard, with none of the effects created by the
processor itself. Compare with wet.
DSP:
Digital signal processing. Broadly speaking, all changes in sound that are produced within a
digital audio device, other than changes caused by simple cutting and pasting of sections of a
waveform, are created through DSP. A digital reverb is a typical DSP device.
dump:
see data dump.
dynamic voice allocation:
A system found on many multitimbral synthesizers and samplers
that allows voice channels to be reassigned automatically to play different notes (often with different
sounds) whenever required by the musical input from the keyboard or MIDI.
early reflections:
A reverb algorithm whose output consists of a number of closely spaced
discrete echoes, designed to mimic the bouncing of sound off of nearby walls in an acoustic space.
echo:
A discrete repetition of a sound, as opposed to reverberation, which is a continuous wash of
closely spaced, non-discrete echoing sound. See delay (3), reverb.
edit buffer:
An area of memory used for making changes in the current patch. Usually the
contents of the edit buffer will be lost when the instrument is switched off; a write operation is
required to move the data to a more permanent area of memory for long-term storage.
editor/librarian:
A piece of computer software that allows the user to load and store patches and
banks of patches (the librarian) and edit parameters (the editor).
effects:
Any form of audio signal processing -- reverb, delay, chorusing, etc.
envelope:
A shape that changes as a function of time. The shape of a synthesizer's envelope is
controlled by a set of rate (or time) and level parameters. The envelope is a control signal that can be
applied to various aspects of a synth sound, such as pitch, filter cutoff frequency, and overall
amplitude. Usually, each note has its own envelope(s).
envelope generator:
A device that generates an envelope. Also known as a contour generator or
transient generator, because the envelope is a contour (shape) that is used to create some of the
transient (changing) characteristics of the sound. See ADSR, envelope.
envelope tracking:
A function (also called keyboard tracking, key follow, and keyboard rate
scaling) that changes the length of one or more envelope segments depending on which key on the
keyboard is being played. Envelope tracking is most often used to give the higher notes shorter
envelopes and the lower notes longer envelopes, mimicking the response characteristics of
percussion-activated acoustic instruments, such as guitar and marimba.
event editing:
An operation in a sequencer in which one musical event at a time is altered.
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