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ABSORPTION
In acoustics, it is the process of some of the energy present in an incident wave, being 'absorbed' by an obstacle. This energy may change into heat and/or mechanical vibration.

ABSORPTION COEFFICIENT
Expresses the 'ability' of a material to absorb energy form an incident sound wave. It has a value ranging from 0 to 1, 0 expressing no absorption and 1 expressing full absorption.

ABFFUSOR:
A panel that both absorbs and diffuses sound.

AC
Alternating Current: current that changes its value cyclically.
 
ACCIACATURA
A grace note in Western staff notation. An acciacatura is written as a small note with a line through it; an acciacatura differs from and appogiatura in that it is usually played very fast, taking as little time out of the subsequent note, to which it is linked, as is possible. It is usually joined by a phrase mark to the subsequent note.

ACCUMULATOR
A logic circuit, which adds a series of numbers, which are fed to it.

ACOUSTICS
The science of sound and acoustic properties. It can also refer to the effect an environment has on a sound.

ACTIVE MOVIE
See ACTIVE-X
 
ACTIVE-X
Allows third party audio effects programmes to work from within wave editors and sequencers in a Windows environment.

ADBDR
Abbreviation for an envelope generator, which has one attack, two decays and releases.
 
ADC
Analogue to Digital Converter. A device that takes Analogue (continuous) electrical signals, and converts them to numerical digital data (discrete). (See also DAC)

ADDITIVE SYNTHESIS
Synthesis process that combines many simple waves (often sine waves) to produce a more complex waveform.

ADSR
Abbreviation for Attack, Decay, Sustain, and Release, the four parameters found on a basic envelope generator; it can also be called a transient generator. The Attack, Decay, and Release parameters are rate or time controls, they effect the time it takes for a change to take place. When a sound is triggered, the envelope generator will rise to its full level at the rate set by the attack parameter, after reaching its peak level it will begin to fall at the rate set by the decay parameter until it reaches the level set by the sustain control. The sustain value indicates a level. The envelope will remain at the sustain level until the key is released when it will return to zero at the rate set by the release parameter.

AES
Audio Engineering Society
 
AES/EBU INTERFACE
A standardised interface for transmitting digital audio between two devices. It employs a shielded twisted pair of wires in a balanced (non-polarised) configuration. It employs RS422 drivers and receivers.

AFTER-TOUCH
Midi controller. Another term used to describe channel or poly key pressure.

ALGORITHM
1.A list of operations needed to carry out a process. 2.A term employed contextually by Yamaha to describe the arrangement of modules in its FM synthesisers.
 
ALIAS, ALIASING
The presence of beat frequencies introduced in a digital audio system if the sampling rate is not high enough for the requirements of the audio bandwidth. The problem can be solved by using an Anti-Aliasing Filter.
 
ALIGNMENT
The process of adjusting the tape heads in a recording machine so that the tape travels in front of it in the correct manner. There are three main adjustments that an engineer needs to carry out on a regular basis:

• WRAP: the tape head is rotated so that the tape skims across the profile of the head symmetrically on either side of the head gap.
• ZENITH: the amount of tilt into or away from the tape is adjusted. It avoids problems of uneven signal output across the head and uneven head wear.
• AZIMUTH: the amount of tilt parallel to the tape path is adjusted. It ensures the tape is perpendicular to the audio track. Avoids phase problems.

ALTERNATIVE NOTATION
Usually refers to graphic extension of Western stave notation.

ALTERNATIVE TUNING
Western instruments are commonly tuned to equal temperament, however there are many alternatives to this system. See also equal temperament and mean temperament

AM
Amplitude Modulation.

AMBIENC:
The distinctive acoustical characteristics of a space.

AMBISONIC SYSTEM
A three dimensional sound reproduction system. It relies on four channels of information, carrying the signals recorded from one omni directional pressure microphone and three pressure gradient, figure of eight microphones.

AMPLIFIER
A line amplifier is designed to operate at medium levels. It's output is in the order of 1 VOLT, A power amplifier is designed to drive a load like a loudspeaker.

AMPLITUDE
Amplitude is a term used to describe the amount of a signal or waveform. It describes the instantaneous magnitude of an oscillating quantity such as sound pressure. It can relate to volume in an audio signal or the amount of voltage in an electrical signal. The peak amplitude is the maximum value.

ANALOG SIGNAL
A current or voltage whose amplitude and frequency vary continuously in direct relationship to the original acoustical or electrical signal. The term describes the fact that the signal is 'analogous' to the original signal.

ANALYSIS
The resolution of a compound object into parts. In music and music technology, there are many and diverse ways of analysing sound. We may break these down into two primary categories; wave analysis and analysis of the music itself.

ANECOIC
Without echo.

ANECOIC CHAMBER
A room designed to minimize internal reflections in a room by employing absorbent materials. It is used for acoustical measurements.

ANSI
American National Standards Institute.
 
ANTI-ALIASING FILTER
A low pass filtered found at the from end of a sampling device. It prevents frequencies above the desired bandwidth to enter the sampling process. It prevents aliasing.

ANTINODE
The part of a vibrating object, which has the widest movement.
 
APPOGIATURA
A grace not in Western notation. An appogiatura differs from and acciacatura in that it is often not played as a quick note. The rules governing how much time these notes take are complex and are open to contextual and historical interpretation.

ARTICULATION
1. A quantative measure of the intelligibility of speech; it is the percentage of speech items correctly perceived and recorded. 2. Describes the way in which a player phrases a piece of music; the degree of legato, staccato or the accentuation.

ARTIFICIAL REVERBERATION
Reverberation achieved by electrical or acoustical means, introduced to simulate that of a particular environment.

ASA
Acoustical Society of America

ASCII
American Standard Code for Information Interchange. A standard set of alphanumeric and control codes which can be represented by a single byte, developed by the USA Standards Institute.

ASHRAE
American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

ASYNCHRONOUS
The term describes data transmission that occurs without an accompanying clock signal. The sending and the receiving device must use the same clock frequency in order for correct transmission to occur.

ATTACK
The beginning of a sound, the initial transient of a musical note. Usually the rise to its maximum value. See ADSR

ATTENUATE
The process of reducing the level, loudness, amplitude or volume of an electrical or acoustical signal. Usually expressed as a ratio or in dB

ATTENUATOR
A device, usually a variable resistance (potentiometer), used to control the level of an electrical signal.

AUDIO DATA COMPRESSION
The process of reducing the amount of stored and/or transmitted digital data used to represent an audio signal. It relies heavily on the principle of masking.

AUDIO FREQUENCY
An acoustical or electrical signal whose frequency falls within the audible range of the human ear, usually accepted as being between 20Hz to 20kHz.

AUDIO-FREQUENCY RANGE
See Audio Spectrum
 
AUDIO SPECTRUM
The range of frequency that human beings can perceive. This is usually accepted as ranging between 20Hz and 20kHz. Many factors affect this, and particularly with age, this range greatly decreases.

AUDITORY AREA
The sensory area lying between the threshold of hearing and the threshold of feeling or pain.

AUDITORY CANAL
The part of the outer ear that connects to the tympanic membrane (eardrum). A canal 25 to 35 mm long.
 
AUDITORY CORTEX
The region of the brain receiving nerve impulses from the ear.

AUDITORY SYSTEM
The human hearing system, comprising the outer, middle and inner ear, the nerve pathways and the brain.

AURAL
Pertaining the auditory mechanism.

AURAL EXCITER
An audio processing device introduced by Aphex in the 1970s. It introduces a certain 'sparkle' to an audio signal. The effect relies on our Psychoacoustics perception and is achieved by comb filtering techniques, selective frequency boosting and narrow band phase shifts.

AUXILIARY SEND:
A set of outputs on a mixing desk that take their signal from the Auxiliary Audio Buss. Each channel on a mixing desk can usually feed a signal on one or more Auxiliary Busses.

A-WEIGHTING:
A frequency response adjustment of a sound-level meter that makes it's reading conform, roughly, to the human response.

AXIAL MODES
Room resonance's associated with each pair of parallel walls.

AZYMUTH ALIGNMENT
See Tape Alignment

AZYMUTH RECORDING
Magnetic recording technique, which reduces crosstalk between adjacent tracks.