Glossary of Audio, Recording and Music Terms "A"

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Absorption – The dissipation of radio or sound waves as they interact with matter. The absorbing of light waves without reflection or refraction.

Absorption Wave Meter – An instrument that is used to measure audio frequencies.

Absolute Phase - A state of audio nirvana in which all equipment and connections between a microphone and the loudspeaker maintain correct polarity. This positive force to the microphone   produces a positive force from the loudspeaker. When two pieces of equipment are interconnected correctly, it can be said that they are “in phase.”

AC - Abbreviation for Alternating Current, an electric current that flows back and forth in a circuit. Studio signals running through audio lines are AC.

Accelerometer – A device measuring the acceleration to which it is subjected and develops a signal proportional to it.

Acorn Tube – Used in low power uhf circuits, this is a small tube with no base and electrodes that are closely connected to its circuits by short wire pins that are sealed in a glass or ceramic envelope. 

Acoustics – The science of sound.

Acoustic Amplifier – A portion of the instrument which makes the vibrating source move air more efficiently; therefore making the sound of the instrument louder. Acoustic amplifiers include the body of an acoustic guitar, the bell of a horn, or a drum’s shell.

Acoustic Echo Chamber - A room equipped with a speaker and microphone that is designed with hard, non-parallel surfaces. Dry signals from the console are fed to the speaker and the microphone will have a reverberation of these signals that can be mixed in with the dry signals at the console.

Acoustical Absorption – The quality of a surface or substance to take in, not reflect, a sound wave.

Active Satellite – Amplifies the received signal and retransmits it back to earth.

Actuator – A part of a switch causing change of the contact connections (e.g.  toggle, pushbutton, or rocker.)

A/D – Analog to Digital Conversion,  the conversion of a quantity that has continuous changes into numbers that approximate those changes. 

ADAT – A trademark of Alesis Corporation designating its modular digital multitrack recording system released in early 1993.

ADSR – Attack, Decay, Sustain and Release, which are the elements of volume changes in the sounding of a keyboard instrument.

AES – Audio Engineering Society.

AES/AES-256 – Advanced Encryption Standard that is used by the US government.

AES/EBU – Audio Engineering Society/European Broadcasting Union, one of the names used as a digital audio transfer standard which is also known as XLR because the AES/EBU digital interface is usually implemented using 3-Pin XLR connectors. This is the same type connector used in a professional microphone. One cable carries both left and right-channel audio data. 

AES/EBU Professional Interface - A standard for sending and receiving digital audio adopted by the Audio Engineering Society and the European Broadcast Union.

Aliasing – A sampler mis-recognizing a signal sent to it that is at a frequency higher than the Nyquist Frequency.  Upon playback, the system will provide a signal at an incorrect frequency (called an alias frequency). Aliasing is a kind of distortion.

Alternating Current – Electric current flowing back and forth in a circuit.

Ambience – The portion of the sound that comes from the surrounding environment rather than directly from the sound source.

Ambient Field – The area away from the sound source where the reverberation is louder than the direct sound.

Ambient Micing – Placing a microphone in the reverberant field (where the reverberation is louder than the direct sound) so as to do a separate recording of the ambience or to allow the recording engineer to change the mix of direct to reverberant sound in recording.

Amp – 1) Short for Amplifier, a device which increases the level of an electrical signal. 2) An abbreviation of Ampere, the unit of current and 3) An abbreviation of amplitude, the height of a wave form above or below the zero line.

Ampere –The unit of current, abbreviated Amp. 

Amplification – An increasing of signal strength.

Amplifier – A device which increases the level or amplitude of an electrical signal, making it louder.

Amplitude – The height of a waveform above or below the zero line.

Analog – Representative, continuous changes that relate to another quantity that has a continuous change. 

Analog Recording – A recording of the continuous changes of an audio waveform.

Analog To Digital Converter – The device which does the conversion of a quantity that has continuous changes (usually of voltage) into numbers that approximate those changes.

Assign – To choose to which place an output is going to be sent.

Assistant Engineer – A Second Engineer is the person who often places microphones, operates tape machines, breaks down equipment at the session end and keeps the paperwork.

Atom – The smallest particle which makes up a specific substance. It's composed of a center around which electrons revolve.

Attack – The rate the sound begins and increases in volume.

Attenuation – A reduction of electrical or acoustic signal strength. 

Audio – Refers to electrical signals resulting from the sound pressure wave being converted into electrical energy.

Automatic Gain Control – A compressor with a long release time used to keep the volume of the audio very constant.

Automation – A console feature that allow the engineer to automate changes i9n the program so that upon playback of the multitrack recording the changes happen automatically.

Aux Send – Abbreviation for Auxiliary Send, a control to adjust the level of the signal sent from the console input channel to the auxiliary equipment through the aux buss.

Auxiliary Equipment – Sound effects devices separate from but working with the recording console.

Axis – A line around which a device operates. For example: In a microphone, this would be an imaginary line coming out from the front of the microphone in the direction of motion of the diaphragm.