Glossary – A
A/B Technique – See “Spaced Pair.”
Absorption – In acoustics, absorption is what happens when sound waves are absorbed by a surface, as opposed to bouncing off the surface (reflection). Absorptive materials in a control room, for example, tend to “deaden” the sound of the room because the sound energy is absorbed rather than reflected. (See also “Reflection.”)
Absolute Phase – This term describes a perfect polarity between an original signal (into the microphone) and the reproduced signal (through the speaker). When positive pressure exerted upon the microphone is translated as positive pressure to the loudspeaker, the two are in “absolute phase.”
AC – See “Alternating Current.”
Accelerometer – A device that measures the acceleration to which it is subjected and creates an electric signal to match it. In music and audio, accelerometers are found in such things as microphones and guitar pickups.
Acorn Tube – Named for its acorn-like shape, an acorn tube is a small vacuum tube used in ultra high frequency (UHF) electronics such as tube amplifiers.
Acoustics – The science of the sound—more specifically, the science of the properties and behavior of sound waves. A good understanding of acoustics is essential to audio engineering and studio design.
Acoustic Amplifier – The part of a musical instrument that vibrates in response to the initial vibration of the instrument, causing the surrounding air to move more efficiently and making the sound louder. For example: the body of an acoustic guitar, the bell of a horn, a drum’s shell, and the wooden soundboard of a piano.
Acoustic Echo Chamber – A room designed with hard, non-parallel surfaces to create reverberation. In recording studios, they are used to add natural reverb to a dry signal.
Active Device – A component that is designed with the ability to control electrical current (as opposed to a “Passive Device”). In the recording studio, active devices are generally components that include an amplifier. (See also “Passive Device.”)
Actuator – The part of a switch that causes change of the contact connections (e.g., toggle, pushbutton, or rocker).
A/D – Abbreviation of Analog-to-Digital Conversion, the conversion of a quantity that has continuous changes (like electrical signals) into numbers that approximate those changes (i.e., computer data).
ADSR – Abbreviation for Attack, Decay, Sustain and Release, the four stages of volume changes in a sound event. ADSR controls are particularly useful on synthesizer instruments.
Additive Synthesis – A method of sound synthesis in which sounds are designed or created by combining simple waveforms together to create richer or harmonically diverse sounds.
AES – Audio Engineering Society.
AES/AES-256 – Advanced Encryption Standard used by the U.S. government.
AES3 – (sometimes called AES/EBU) A digital audio transfer standard developed by the Audio Engineering Society and the European Broadcasting Union for carrying dual-channel digital audio data between devices. AES3 is the protocol behind XLR cables, as well as RCA and S/PDIF cables.
Aftertouch – (Also called “Pressure Sensitivity“) A feature in some keyboard instruments by which applying additional pressure to a key after it has been pressed can activate an additional MIDI control command. a synthesizer or Keyboard Controller of After Touch (a control or operational function of a synthesizer where pressing a key after it has been pressed, and before it is released, will activate a control command that can be set by the player).
Aliasing – A type of digital signal distortion that occurs in a sampler when the incoming signal frequency exceeds the Nyquist frequency for that unit. The sampler reproduces it at an incorrect frequency, or an “alias,” causing a distortion or artifact in the sound. (See also “Nyquist Frequency.”)
Alternating Current (or AC) – The type of electrical current found in standard electrical outlets and studio signals running through audio lines. In AC, the current “alternates” directions, flowing back and forth through the circuit.
Ambience – In most cases, this refers to the “atmosphere” of a certain place, like a restaurant. But in recording, it refers to the part of the sound that comes from the surrounding environment rather than directly from the sound source. For example, the sound waves coming into your ears from a cello being played are coming directly from the source, but the sound of the same cello coming to you after bouncing off the back wall is ambient sound.
Ambient Field – The area away from the sound source where the reverberation is louder than the direct sound.
Ambient Miking – This refers to placing a microphone in the ambient field of a room to record the ambient reverberations of the sound. The recording engineer often does this in addition to direct micing of the instrument(s) to create a blend or mix of direct and reverberant sound in the recording.
Amp – An abbreviation for “Amplifier,” “Amplitude” or “Ampere,” depending on context. (See below.)
Ampere – The unit of measure for electrical current, abbreviated Amp.
Amplifier – A device that increases the level or amplitude of an electrical signal, making the resulting sound louder.
Amplitude – The height of a waveform above or below the zero line. In audio, this usually translates to the signal strength or the volume of the sound.
Analog – A continuously changing representation of a continuously variable quantity. In the context of audio, this refers to using continuously changing electrical signals (voltage) to represent the continuously variable frequencies of sound, and/or recording those signals to an analog medium. Analog is in contrast to digital, which represents constantly changing quantities in the form of fixed numeric values.
Analog Recording – A recording of the continuous changes of an audio waveform. The most common example of analog recording in a recording studio is recording on reel-to-reel magnetic tape.
Analog To Digital Converter (A/D) – A device that translates a continuously changing signal (analog) into numeric values that approximate those changes (digital). In audio recording, this refers to converting recorded sound from electrical voltages to computerized data.
Attack – The initiation of a sound. In terms of the four stages of a sound (Attack, Decay, Sustain and Release, or ADSR), a sound’s attack is the point where the sound begins and increases in volume to its peak.
Attenuation – The reduction of electrical or acoustic signal strength. In audio, attenuation is measured in decibels (dB) and is typically heard as a reduction in volume. Sound waves traveling through the air naturally attenuate as they travel away from the source of the sound. Engineers also purposefully attenuate signals in the studio through gain controls or pads to prevent overload.
Audio – In its broadest sense, audio is the range of frequencies we humans can hear with our ears. In the technical sense, audio refers to the transmission, recording or reproduction of sound, whether digitally, electrically or acoustically.
Automatic Dialogue Replacement (ADR) – The process of re-recording dialogue for film in a controlled environment after the film is shot, for the purpose of replacing poorly recorded dialogue.
Automatic Gain Control – A compressor with a long release time, which is used to keep the volume of the audio at a consistent level.
Automation – Programming certain changes to occur automatically during recording and/or playback. In the studio, engineers use automation on their consoles or computers so various parameters will change automatically at different times during multitrack recording and playback. This pre-programming feature makes it easier to create those changes than attempting to perform them all manually in real time.
Auxiliary Return – (Abbreviated Aux Return or Return) The input on a console or DAW that returns the effected signal sent through the auxiliary send back into the channel mix.
Auxiliary Send – (Abbreviated Aux Send or Send) A control to adjust the signal level being sent from the input channel on a console or DAW to auxiliary equipment or plug-ins through the auxiliary bus. This is typically used for creating an effects loop that processes a portion of the signal, then returns it into the mix through the auxiliary return.
Auxiliary Equipment – External signal processing devices that work alongside the mixing console to modify the signal.
Axis – An imaginary line around which a device operates. For example: in microphone use, the axis is an imaginary line coming out from the front of the microphone in the direction of motion of the diaphragm, delineating the optimum location for the mic to pick up the sound. Sounds that occur “off-axis” from the microphone will not be picked up as clearly.