Glossary: Absorption Coefficient

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Absorption Coefficient: Represented by the Greek letter Alpha, a measure of the relative amount of energy that will be absorbed when a sound hits a surface. Absorption coefficients are always a value ranging from 0 to 1 that when multiplied by the surface area in question yield a percentage of sound that will be absorbed by that surface. This percentage is in units known as Sabins, after the Harvard professor and acoustician, Wallace Sabine. An absorption coefficient of 1 means that all acoustic energy striking the surface will be absorbed and none reflected. A coefficient of 0 means that all the energy is reflected. The latter condition is virtually impossible and the former condition is rare. The absorption coefficient varies by frequency because most materials have different absorption characteristics at different frequencies. Acousticians use absorption coefficients to help determine the RT-60 or reverberation time of rooms, and as such many common building materials have been measured and results published for their absorption coefficients.

A & R	A-B Stereo	A-Time
A-weighted	A440	AAC - Advanced Audio Coding (also MPEG-2 AAC)
AAF	Abalone	ABS
Absolute Phase	Absorption	Absorption Coefficient
Alternating Current (AC)	AC-1	AC-2
AC-3	Academy Curve	A cappella
Accent	Access Time	Accidental
Accompaniment	Accumulator	Acetate
Acoustic Lens	Acoustic Suspension	Acoustic Treatment
ACPI	Action	Actionflo
Active	Active Sensing	Actuator
Adagio	ADAT	ADAT/FST
ADAT Optical	ADB	A/D Converter (ADC)
Additive Synthesis	Adjusto-Matic	ADPCM
ADR	ADSR	Aeolian Harp
Aerophone	AES	AES/EBU
AES3	AES3id	AES42-2001
AFL	AFM	Aftertouch
AFTRA	AGC	Aggregate Device
Aging Toner	Agitato	AGP
AHDSFR	AIFF (Audio Interchange File Format)	AIR
AIT	Alder	Alder
Aleatoric Music (Composition)	Algorithm	Alias
Aliasing	Alkaline Battery	All-Button Mode
All-Notes-Off	Allegro	Alnico
Alteration	Altered Chord	Alternate Tuning
Alto	AM	Ambience
Ambisonics	Amen Break	Amperage
Ampere	Amp Head	Amplifier
Amplifier, Instrument	Amplitude	AMS
Analog	Analog Sequencer	Analog Synthesizer
Anamorphic	Andante	Anechoic
Anode	Anodize	Anodized
ANSI	ANSI A-Weighting	Antecedent and Consequence
Antenna	Antenna gain	Anti-Imaging Filter
Anti-Aliasing Filter	Anti-node	Aperiodic
API	Apoyando	Apple Talk
Application (Program)	Architecture	Archival Stability
Archtop Guitar	Arco	ARP Avatar
Arpeggiator	Arpeggio	Arrangement
Articulation	Artificial (or Automated) Double Tracking or ADT)	ASCAP
ASCII	Ash	Ashtray Bridge Cover
ASIC (Application Specific Integrated Circuit)	ASIO	Aspect Ratio
Asperity	ASPI	Asynchronous
ATA	ATA-2	ATA 66/100/120
ATAPI	Absolute Time Code	Atonal Music
ATRAC	ATRAC	Attack
Attenuation	Audio	Audiobook
Audiology	Audio RIP	Audio Suite
AudioUnits	Audiowire	Auditory Cortex
Augmented Interval	Auranomic	Author
Authorize	Auto Accompaniment	Autolocate/Autolocator
Automata	Automatic Mixer	Automation
Auto Punch	Aux Send	AVI
AWG (American Wire Gauge)	AWM	Axe