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A440: Musical term that refers to the pitch A above Middle C having a frequency of 440Hz, or cycles per second. This is sometimes referred to as "Concert Pitch." Following the principles of equal temperament, A440 means that the C above it has a frequency of approximately 523.3Hz. A standardized Concert Pitch is essential for musicians to play instruments together in tune. Some form of standard pitch has been around ever since two individuals wished to sing or play two instruments together. Sometime after 1200 AD, vocal groups (usually monks) and whatever instrumental ensembles existed used a pitch pipe to provide a reference tone for tuning. In 1711the tuning fork was invented. At that time, it had a pitch of A423.5. This points out that Concert Pitch has not always equaled A440. In fact, it has varied widely through history. From the 17th century forward the reference "A" has ranged from a low of 373.7Hz to a high of 457.6Hz. The differences can be loosely described this way: a lower tuning results in a "darker" sound, while a "brighter" timbre is attributed to a higher tuning. In1936 the American National Standards Institute (a scientific group, not a musical one) adopted 440Hz. In 1939 A440 was adopted internationally and it has remained the standard since then. Some pitch standards have risen a little, particularly in Eastern European countries, in which pianos are often tuned to A444 or even a bit higher. Some concert halls in the UK and European countries have two pianos on site, one tuned to A440 and one tuned to A444. This satisfies the desires of performers and keeps the pianos stable.

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	Agoya
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
Amplitude Modulation	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	Axial Room Mode