Audio Glossary

30 Aug 2016

A/D Converter: Analog to digital converter, a device that transforms incoming analog signals into digital signals.

AFL: An acronym for After Fade Listen, another way of saying post-fader solo.

Aux Send: A mixer bus output designed to send a signal to an auxiliary processor or monitor system.

Aux Return: A mixer input with limited control capabilities, intended for bringing the output of an auxiliary processor or other line-level source into the main mix bus.

Balanced Input: An input consists of two leads, neither of which is common to the circuit ground. This is a “differential pair”, where the signal consists of the difference in voltage between the two leads. Balanced input circuits can offer excellent rejection of common-mode noise induced into the line.

Balanced Output: In a classic balanced audio circuit, the output is carried on two leads (high/+ and low/-) which are isolated from the circuit ground by exactly the same impedance. A symmetrical balanced output carries the same signal at exactly the same level but of opposite polarity with respect to ground. A special case of a balanced output carries the signal on only one lead, with the other lead being at zero voltage with respect to ground, but at the same impedance as the signal-carrying lead.

Bandwidth: The band of frequencies that pass through a device with a loss of less than 3dB, expressed in Hertz or in musical octaves.

Cardioid: Heart-shaped. In sound work, cardioid refers to the shape of the sensitivity vs. direction plot for a particular style of directional microphone. A cardioid mic rejects sound arriving from the rear.

Channel: A functional path in an audio circuit: an input channel, an output channel, a recording channel, the left channel and so on.

Channel strip: The physical realization of an audio channel on the front panel of a mixer.

Clipping: A form of severe audio distortion that results from peaks of the audio signal attempting to rise above the capabilities of the amplifier circuit. To avoid clipping, reduce the system gain in or before the gain stage in which the clipping occurs.

Compressor: This is a dynamic processor used to smooth out any large transient peaks in an audio signal that might otherwise overload your system or cause distortion. The amplitude threshold and other parameters such as attack time, release time, and ratio are adjustable.

Condenser: Condenser microphones require electrical power to run internal amplifiers and maintain an electrical charge on the capacitor. They are typically powered by internal batteries or “phantom power” supplied by an external source, such as a mixing console.

Cueing: In broadcast, stage and post-production work, to “cue up” a sound or video source (a record, a sound effect on a CD, a song on a tape) means to get it ready for playback by making sure you are in the right position on the “cue,” making sure the level and EQ are all set properly. This requires a special monitoring circuit that only the mixing engineer hears. It does not go out on the air or to the main mixing buses. Cueing can also refer to a similar process regarding video playback.

D/A converter: Digital-to-analog converter, a device that transforms incoming digital signal into analog form.

Decibel (dB): A unit used to measure the intensity of a sound or the power level of an electrical signal by comparing it with a given level on a logarithmic scale.

Delay: In sound work, delay usually refers to an electronic circuit or effects unit whose purpose it is to delay the audio signal for some short period of time. Delay can refer to one short repeat, a series of repeats or the complex interactions of delay used in chorusing or reverb. When delayed signals are mixed back with the original sound, a great number of audio effects can be generated, including phasing and flanging, doubling, Haas precedence-effect panning, slap or slapback, echo, regenerative echo, chorusing and hall-like reverberation. Signal time delay is central to many audio effects units.

Dry: Usually means without reverberation, or without some other applied effect like delay or chorus.

Dynamic microphone: The class of microphones that generate electrical signals by the movement of a coil in a magnetic field. Dynamic microphones are rugged, relatively inexpensive, capable of very good performance and do not require external power.

Equalization (EQ): Refers to purposefully changing the frequency response of a circuit, sometimes to correct for previous unequal response (hence the term, equalization), and more often to boost or cut the level at certain frequencies for sound enhancement, to remove extraneous sounds, or to create completely new and different sounds.

Frequency: The number of times an event repeats itself in a given period of time. The audio frequency range is generally considered to be 20 Hz to 20, 000 Hz. This covers the fundamental pitch and most overtones of musical instruments.

Gain: The measure of how much a circuit amplifies a signal. Gain may be stated as a ratio of input to output voltage, current or power, such as a voltage gain of 4, or a power gain of 1.5, or it can be expressed in decibels, such as a line amplifier with a gain of 10dB.

Gate: A dynamics processor that automatically turns off an input signal when it drops below a certain level. This can reduce the overall noise level of your mix by turning off inputs when they are not in use. Threshold, attack time, hold, and release time are some of the adjustable gate parameters.

Graphic EQ: A graphic equalizer uses slide pots for its boost/cut controls, with its operating frequencies evenly spaced through the audio spectrum. In a perfect world, a line drawn through the centers of thecontrol shafts would form a graph of the frequency response curve.

Ground: Also called earth. Ground is defined as the point of zero voltage in a circuit or system, the reference point from which all other voltages are measured.

• In electrical power systems, ground connections are used for safety purposes, to keep equipment chassis and controls at zero voltage and to provide a safe path for errant currents. This is called a safety ground. Maintaining a good safety ground is essential to prevent electrical shock.
• In sensitive electronic equipment, tiny currents and voltages riding on the ground (so it’s not truly zero volts) can cause noise in the circuits and hamper operation. Often a ground separate from the power ground is used as the reference point for the electronics, isolating the sensitive electronics from the dirty power ground. This is called a technical ground. Hertz: The unit of frequency, equal to 1 cycle per second. Abbreviated Hz. kHz = 1000 Hz, and is usually pronounced “kay” (with “Hertz” implied) by sound professionals who ask for “a little more two and a half K” when they want you to boost 2.5 kHz (2500Hz).

Impedance: A measure of the AC resistance, capacitance, and inductance in an electrical circuit, measured in ohms;; all of these three properties impede the flow of current. AKA: the higher the impedance, the lower the current. In audio circuits (and other AC circuits) the impedance in ohms can often be much different from the circuit resistance as measured by a DC ohmmeter. Maintaining proper circuit impedance relationships is important to avoid distortion and minimize added noise. Level: Another word for signal voltage, power, strength or volume. Audio signals are sometimes classified according to their level. Commonly used levels are: microphone level (-40 dBu or lower), instrument level (-20 to -10 dBu), and line level (-10 to +30 dBu).

Line level: A signal whose level falls between -10 dBu and +30 dBu.

Main (house) speakers: The main loudspeakers for a sound reinforcement system. These are usually the largest and loudest loudspeakers, and are usually positioned so that their sound seems to come from the area of the main stage.

Master: A control affecting the final output of a bus on which one or more signals are mixed. A mixer may have several master controls, which may be slide faders or rotary controls.

Mic level: The typical level of a signal from a microphone. A mic level signal (usually but not always coming from a microphone) is generally lower than -30 dBu. With a very quiet source (a pin dropping?) the signal can be -70 dBu or lower.

Mic preamp: Short for microphone preamplifier. An amplifier whose job is to bring the very low microphone level signal up to line level, or in the case of a mic preamp built into a mixer, the mixer’s internal operating level (approximately 0 dBu). Mic preamps often have their own volume control, called a trim control, to properly set the gain for a particular source. Setting the mic preamp gain correctly with the trim control is an essential step in establishing good signal-to-noise ratio and sufficient headroom for your mix.

Monitor: In sound reinforcement, monitor speakers (or monitor headphones or in-the-ear monitors) are those speakers used by the performers to hear themselves. In recording, the monitor speakers are those used by the engineer and production staff to listen to the recording as it progresses.

Noise: Whatever you don’t want to hear. Could be hum, buzz or hiss;; could be crosstalk or digital hash or your neighbor’s stereo;; could be white noise or pink noise or brown noise.

Normal: A wiring method which electrically ties together two jacks or two poles of one jack so that in normal operation, there is signal flow between them. Inserting a plug breaks this connection, allowing the signal path to be modified. Normal wiring is common in patchbays and insert jacks.

PA: Acronym for Public Address. An electronic amplification system used as a communication system in public areas. Today, people who work with PA systems like to say they’re working in “sound reinforcement”. Pan, pan pot: Short for panoramic potentiometer. A pan pot is used to position (or even dynamically move) a monaural sound source in a stereo mixing field by adjusting the source’s volume between the left and right channels.

Patch bay: A collection of usually a large number of jacks allowing convenient access to various points in a system’s interconnect wiring. A patch bay can make re-routing signals very convenient without having to fish around with cables in the back of racks or consoles.

Parametric EQ: A “fully” parametric EQ is an extremely powerful equalizer that allows smooth, continuous, and independent control of each of the three primary EQ parameters: frequency, gain, and bandwidth.

PFL: An acronym for Pre Fade Listen. Sound folks call it being able to solo a channel with the fader down.

Phantom Power: A system of providing electrical power for condenser microphones (and some electronic pickup devices) from the microphone input jack;; it provides +48V across two pins in a 3-pin XLR. The system is called phantom because the power is carried on standard microphone audio wiring in a way that is “invisible” to ordinary dynamic microphones. Generally, phantom power is safe to use with non-condenser microphones as well, especially dynamic microphones. However, unbalanced microphones, some electronic equipment (such as some wireless microphone receivers) and some ribbon microphones can short out the phantom power and be severely damaged. Be careful!

Phase: The time relationship between two signals, expressed in degrees around a circle. 0 and 360 degrees represents an in-phase relationship – both signals change in the same way at the same time. Anything else is out of phase. 180 degrees out of phase is a special case which, for a continuous waveform, means that at any given time the two signals have the same amplitude but are opposite in polarity. The phase reverse switch found on some mixers or mic preamps actually reverses the signal polarity. When out-of-phase signals are mixed, there will be some cancellation at certain frequencies, the frequencies and the degree of cancellation being a function of the amount of phase shift and the relative amplitude of the signals. Attention to mic placement and careful listening will allow you to use this effect creatively.

Post-fader: A term used to describe an aux send (or other output) that is connected so that it is affected by the setting of the associated channel fader. Sends connected this way are typically (but not always) used for effects.

Pre-fader: A term used to describe an aux send (or other output) that is connected so that it is not affected by the setting of the associated channel fader. Sends connected this way are typically (but not always) used for monitors.

Return: A return is a mixer line input dedicated to the task of returning processed or added sound from reverb, echo and other effects devices. Depending on the internal routing of your mixer and your own inclination, you could use returns as additional line inputs, or you could route your reverb outputs to ordinary line inputs rather than the returns.

Reverb: The sound remaining in a room after the source of sound is stopped. Reverberation and echo are terms that are often used interchangeably, but in audio parlance a distinction is usually made: reverberation is considered to be a diffuse, continuously smooth decay of sound, whereas echo is one or more distinct, recognizable repetitions of a word, note, phrase or sound which decreases in amplitude with every repeat. Highly reverberant rooms are called live;; rooms with very little reverberation are called dead. A sound source without added reverb is dry;; one with reverb or echo added is wet.

Signal-to-noise ratio: This is a specification that describes how much noise an audio component has compared to the signal. It is usually expressed in dB below a given output level.

Surround sound: Multi-channel audio playback systems in 6, 8, or 10-channel formats. Surround sound is typically found in movie theaters and home theater systems.

TRS: Acronym for Tip-Ring-Sleeve, the three parts of a two-conductor (plus shield) phone plug. Since the plug or jack can carry two signals and a common ground, TRS connectors are often referred to as stereo or balanced plugs or jacks.

TS: Acronym for Tip-Sleeve, the two parts of a single conductor (plus shield) phone plug. TS connectors are sometimes called mono or unbalanced plugs or jacks.

Unbalanced: An electrical circuit in which the two legs of the circuit do not have the identical impedance to ground. Often one leg is also at ground potential. Unbalanced circuit connections require only two conductors (signal “hot” and ground). Unbalanced audio circuitry is less expensive to build, but under certain circumstances is more susceptible to noise pickup.