Apr 14, 2005 1:33 PM

AES/EBU DIGITAL STANDARD: developed jointly by the Audio Engineering Society (AES) and the European Broadcast Union (EBU). The standard describes a format for transmitting two channels of digital audio along a serial cable. See S/PDIF.

AES: the Audio Engineering Society, a professional association of sound engineers headquartered in New York City, with chapters throughout the world. Sponsors large annual conventions showcasing new audio technologies and products.

AMPLIFIER: a device that tracks the amplitude of an incoming signal and proportionally increases the voltage, current or power of the signal by adding power from another source.

ANALOG-TO-DIGITAL CONVERTER (ADC): a circuit or hardware peripheral that converts audio signals from the analog domain into a digital form.

ANALOG: in recording, a signal that is stored as a continuously varying electrical representation (analog) of the input signal.

ATTENUATION: the process of decreasing the amplitude of a signal as it passes from one point to another. Analog attenuation circuits typically use resistors to reduce the voltage of a signal. In audio, the effect of such attenuators is usually expressed in decibels.

AUX SEND: alang for auxiliary send, a circuit pathway in a mixing console that supplies an independent mix, which can be routed to an external (auxiliary) device such as an effects processor or monitor system. Most modern consoles have several aux sends on each input so several devices can process a sound. See bus.

BALANCED LINE: an audio line comprising three conductors: two carrying signal and a ground (shield) wire, in which one of the signal wires carries the sound, while the other carries an inverted copy. When the signal reaches the destination, the inverted copy is flipped and added to the original. Any noise that has been induced into the signal is also inverted. When this is combined with the "un-inverted" noise, it cancels it out. Thus, balanced lines are less susceptible to hum and can carry audio signals over longer distances. Balanced audio lines typically use 3-pin XLR or 1/4-inch tip-ring-sleeve phone connectors.

BIT: Short for binary digit, this is a single piece of information (expressed as either 0 or 1) in a computer or digital system.

BUS: an internal pathway for audio signals in a console. Frequently misspelled "buss."

CLIPPING: a distortion condition in which the top of a waveform is cut off ("clipped"). This is usually caused when a signal overloads a stage of the device being driven.

CLOCK: a source of timing information, especially important when two or more devices must be synchronized. See synchronization.

COMPRESSOR: a device that smoothes the level of an input signal by regulating its dynamic range. A compressor prevents the signal from rapidly exceeding or falling below a selected amplitude threshold. Beyond the threshold, the ratio of the signal's input level to output level (e.g., 2:1, 4:1,= and so on) can be user-selected. Compression is commonly used to keep mic levels within an acceptable range. Because it can slow a signal's rate of decay below the threshold, compressors are also used to add sustain to instruments such as electric guitar and bass.

CONDENSER MICROPHONE: a microphone that picks up sounds via an electrically charged, metallized diaphragm, which is separated from a conductive back plate by a thin air layer. Sound waves striking the diaphragm cause a minuscule voltage change, which is increased by a tiny amplifier circuit within the mic body. Because power is required by both the microphone capsule and the amplifier, condenser microphones must have a power source, which can be a battery inside the mic body or "phantom" power from a mixing console or external power supply.

CUE MIX: See monitor mix.

DAW: abbreviation for digital audio workstation, a generic name for a computer-based system of recording, editing and manipulating audio in the digital domain.

dB: abbreviation for "decibel." See decibel.

dBm: a term expressing an electrical power level, referenced to 1 milliwatt (i.e., 0 dBm = 1 mW). Originally, dBm was used to express the power dissipated in telephone applications with 600-ohm impedances, but it is not necessarily referenced to a particular impedance.

dBu: a means of expressing voltage, referenced so that 0 dBu equals 0.775 volts, regardless of impedance. 1 mW of power is dissipated if 0.775 volts is applied to a 600-ohm load, so when the load impedance is 600 ohms, 0 dBu = 0 dBm.

dBV: a means of expressing voltage, referenced so that 0 dBV equals 1-volt RMS, regardless of impedance.

dBv: synonymous with dBu, but rarely used due to confusion with dBV. See dBu.

DCA: abbreviation for "digitally controlled amplifier," which is an amplifier circuit whose output gain can be varied by a digital signal.

DECIBEL: a unit of measure used to logarithmically express ratios of change in power or signal levels. Equal to one-tenth of a Bel (named for Alexander Graham Bell).

DIGITAL: computer technology in which information is described as a series of (usually binary) numbers.

DIGITAL-TO-ANALOG CONVERTER (DAC): a device that converts audio from the numeric string of a digital representation to an analog signal of constantly fluctuating voltages.

DIGITALLY CONTROLLED AMPLIFIER: See DCA.

DIM SWITCH: a switch near a console's master section that reduces (attenuates) playback level by a set level (usually 15 or 20 dB), and is often used to momentarily cut the playback level during control room conversations, answering phone calls, etc.

DYNAMIC MICROPHONE: a transducer that relies on the law of induction, with an output proportional to the velocity of a moving element within a magnetic field. The most common type is the moving-coil microphone, which picks up sounds when sound waves strike a diaphragm attached to a coil of wire. When the coil moves within the magnetic structure of the microphone, it creates an output voltage. The process is exactly the reverse of the way a speaker operates. Moving-coil dynamic microphones tend to be extremely rugged, making them well suited for most sound reinforcement applications. The other common type of dynamic microphone is the ribbon mic.

DYNAMIC RANGE: a ratio (expressed in decibels) of the difference between the softest and the loudest sound that can be produced, reproduced or captured by a musical instrument or audio device.

ECHO: the effect of a sound reflecting off a distant surface and returning to the source. Typically, an echo is defined as a delay lasting more than 50 milliseconds (0.05 seconds).

ECHO SEND: a console bus that allows the engineer to route a variable part of a channel's signal to an effects device. Also sometimes called reverb sends or post-fader sends.

EQUALIZATION: a circuit that allows the frequency-selective manipulation of a signal's amplitude. The simplest equalizers are shelving types, offering the ability to cut or boost gain above or below a given frequency. Examples include the treble and bass controls found in home stereo systems or guitar amps. More complex circuits that allow tonal shaping in multiple frequency bands include graphic and parametric equalizers. Abbreviated "EQ."

FEEDBACK: a condition in which the output of a circuit recycles through its input. Acoustic feedback is a whine or howl that occurs in live audio situations when an amplified sound re-enters a sound system through the same microphone (or guitar pickup) that reproduced the original source, creating a loop.

FREQUENCY: the number of times a periodic waveform cycles, or repeats, over a period of time. See hertz.

GAIN: a ratio expressing the difference between the input and output power, level or current in a circuit.

GATE: a device that opens or closes a pathway by stopping signals that fall below a user-defined level. Audio gates often are used to salvage noisy tape tracks and silence "dirty" sound systems: The gate stays closed—blocking residual, low-level noise—until the audio signal's level exceeds a user-determined threshold. Then, the gate opens, allowing the sound to be heard. Gates can also be used to create effects such as gated reverb.

GRAPHIC EQUALIZER: a frequency-shaping device having multiple filter bands, each operating at a fixed frequency and bandwidth.

GROUND LOOP: a condition that occurs when several ground pathways exist between two devices, resulting in hum and increased noise.

HEADROOM: the margin of safety (usually expressed in decibels) between nominal operating levels and a signal-overload condition.

HERTZ: a unit of measure of the frequency of a vibrating object, such as a guitar string, speaker cone or electrical signal. Equivalent to cycles per second, it is named for Heinrich Hertz and abbreviated "Hz."

HIGHPASS FILTER: a circuit designed to attenuate, or cut, frequencies that fall below some designated point, while allowing higher frequencies to pass unaffected.

IN-EAR MONITOR: a system allowing onstage players to listen through earphones rather than floor monitor speakers. Often abbreviated as IEM.

I/O: abbreviation for "input/output."

JACK: a "female" connector designed to "mate" with a "male" connector or plug.

K: symbol for "kilo" in computer applications, in which a kilo represents 1,024 rather than 1,000. For example, one kilobyte (1 KB) equals 1,024 bytes. See byte.

k: scientific symbol for "kilo" (1,000). For example, a standard test tone is 1,000 Hz, which also can be stated as "1 kHz."

LIMITER: a device that severely restricts the upper dynamic range of a signal, regulating the rate of increase of an input signal's amplitude to keep it from exceeding a pre-determined threshold. Limiters are closely related to compressors but apply much higher compression ratios, usually in excess of 20:1.

LINE-LEVEL: an input or output operating level, typically -10 dBV for home and semi-pro equipment and +4 dBm for professional gear. Typical line-level audio signals include synth outputs, mixer outputs and signal processor outputs.

MADI: acronym for "multichannel audio digital interface," a professional standard for transmitting up to 56 channels of digital audio data over a single cable.

MATRIX MIXER: a specialized submixer built into sound reinforcement consoles that allows the engineer to create multiple dedicated mixes for applications such as lobby audio, subwoofers, underbalcony fills or separate feeds to individual clusters or zones in a venue.

MEGABYTE: a quantity of computer data or memory capacity equal to 1,024 kilobytes, or 1,048,576 (1,024x1,024) bytes. Abbreviated "MB."

MIDI MACHINE CONTROL: a protocol for using MIDI commands, often from a console/controller surface, to control the transport functions (stop/play/record/locate/rewind/fast-forward) of a tape recorder/workstation.

MONITOR MIX: one or more simultaneous mixes—live or in the studio—created to help performers hear while they perform. Sometimes referred to as "cue mixes" in the studio.

MUTE: a control that interrupts ("mutes") the flow of a signal. For example, during a mixing session, a console with muting would allow the engineer to silence a noisy guitar track during a quiet introduction and activate it just before the guitar part begins. Some mixers offer the ability to automate mutes.

NOISE GATE: See gate.

NYQUIST THEOREM: the basic tenet in digital audio systems, stating that the highest throughput frequency in a sampling system must be equal to or less than one-half the sampling frequency. Theoretically, the highest frequency reproducible (without generating undesirable aliasing noise) by a system operating at a sampling rate of 48 kHz is 24 kHz. In practice, with the need for brickwall anti-aliasing filters, the actual upper-frequency response of such a system is somewhat less.

OHM'S LAW: The basis for nearly all electronic and electrical theory, this law states a constant relationship between voltage, current and resistance. In a circuit, the voltage across an element is equal to the current in amperes through the element, multiplied by that element's resistance in ohms. Mathematically, this is expressed as E = IR, where E is the voltage, I is the current and R is the resistance.

PANNING: the ability to place a monaural signal at any point in the stereo soundfield of a stereo signal using amplitude clues for localization. Short for "panorama," a pan control on a mixing board is a rotary control where the extreme counterclockwise position routes a signal to the left-channel output, the extreme clockwise position routes the signal to the right and the center position sends the signal equally to the right and left sides.

PARAMETRIC EQUALIZER: a circuit designed for frequency-selective attenuation or boosting of a signal's amplitude, with independent controls for gain, center frequency and bandwidth (including continuously adjustable Q). A quasi-parametric EQ may provide full frequency and gain adjustment, but only two or three Q settings. Sweepable EQs have an adjustable (sweepable) center frequency, but operate on a fixed bandwidth.

PATCHBAY: a central routing center for signals, such as audio, video or MIDI data. While patchbays have traditionally used short cables (called patch cords) to route signals to various points on a panel of jacks, they have been evolving slowly into microprocessor-controlled devices that handle and store signal routings electronically.

PHANTOM POWER: a method of powering condenser microphones by sending DC current (typically 9 to 52 volts) over the same mic cable that carries the audio signal. "Phantom" is derived from the fact that there is no visible power cord and the voltage is not perceptible in the audio path.

PHASE: the relative measurement of a period of time referenced to the start point of a cycle of a periodic waveform. In one complete period, a wave's polarity fluctuates 360 degrees (180 degrees positive and 180 degrees negative). Absolute phase is a reference point in time within one cycle; e.g., halfway through one period, the waveform's phase is 180 degrees. At one-quarter of the waveform, the phase is 90 degrees. Relative phase is an instantaneous ("snapshot") measure of the difference in time between two acoustic or electronic waveforms of the same waveform and frequency. For example, if one waveform is one-quarter of the way through its cycle (90 degrees at its peak positive value) and the other is three-quarters of the way through its cycle (270 degrees at its greatest negative value), they are 180 degrees out-of -phase with respect to each other. The two signals are "in phase" if their amplitudes are identical at the same point in their cycles. Console inputs often have "phase" switches (more correctly, these should be referred to as "polarity" switches), which invert the phase of the signal 180 degrees.

PHASE CANCELLATION: an attenuation of signal components resulting from combining out-of-phase waveforms. When two waveforms are mixed, their harmonics are added. If the signals are out-of-phase with each other, the amplitudes of the harmonic components differ at various times (as determined by the phase relationship). If the added harmonics have the same polarity, then the signal is reinforced at those frequencies. If harmonics with positive values are added to harmonics with negative values, then the signal is attenuated (canceled) at those frequencies.

PHONE CONNECTOR: a connector based on a plug having a shaft 1/4 inch in diameter. Commonly used as audio connectors on electric guitars, synthesizers and "semi-pro" signal processors and mixers. Originally developed by Bell Telephone; hence, the "phone" name.

PHONO CONNECTOR: Sometimes referred to as an RCA connector, these are generically known as pin-jack connectors. Commonly used on home stereo equipment, the "phono" designation for these audio connectors comes from the fact that they originally were universally used for the outputs on phonographs.

PINK NOISE: a test signal comprising noise that has been shaped to provide equal intensities of sound in each octave band. Pink noise is used for test signals because its spectral balance closely compensates for the frequency sensitivity of the human ear.

POST-FADER SEND: Sometimes called an "effects send," this refers to a console auxiliary send that is connected after ("post") a channel's output fader. For example, if a post-fader send is used to route part of a vocal track to a reverb, when the vocal channel's level is raised with the fader, the amount sent to the reverb also would increase. See pre-fader send.

POTENTIOMETER: an electronic component comprising two terminals connected to either end of a resistive element and a conductor that can be moved between the two ends, thus allowing the creation of a variable resistor or voltage divider. Potentiometers are most often rotary controls (such as volume controls), but also exist as linear controls, such as faders or sliders. Often called a "pot."

PRE-FADER SEND: Sometimes called a "monitor" (or "foldback") send, this refers to a console auxiliary send that is connected before ("pre") a channel's output fader. For example, if a pre-fader send is used to route part of a vocal track to a stage monitor, when the main vocal channel's level is raised, the amount sent to the monitor would be unchanged. See post-fader send.

RACKMOUNT: equipment designed to fit industry-standard, 19-inch-wide equipment racks and cases. The height of rackmount gear is standardized in 1.75-inch "units": a 2U (2-unit) device is 3.5 inches tall, a 10U mixer is 17.5 inches tall, etc.

RCA CONNECTOR: See phono connector.

ROLL-OFF FILTER: a circuit that attenuates a signal that is above (lowpass filter) or below (highpass filter) a specified frequency. For example, microphones frequently have a bass roll-off filter to remove wind noise and/or excessive breath pops.

ROM: bacronym for read-only memory, a non-erasable chip or circuit capable of storing computer data.

SAMPLING FREQUENCY: See sampling rate.

SAMPLING RATE: Also referred to as sampling frequency, this is the rate at which "snapshots" of an analog signal are converted into digital representations. The higher the sampling rate, the greater the accuracy of a digital reproduction. See Nyquist Theorem.

SIGNAL-TO-NOISE RATIO: a ratio (in decibels) that expresses the difference between the level of a signal at a reference point in a circuit and the level of electrical noise at the same point.

SOLO: a feature on a mixing console that automatically routes one or more selected channels to the recording monitors or headphones without disturbing the main audio mix. For example, if a buzzing sound is heard while recording a drum/piano/bass rhythm section in the studio, an engineer can push the solo button on several tracks to locate the offending instrument. Some studio consoles use destructive solo, where the solo’ed instruments replace the mix in the main stereo bus. On sound reinforcement mixing consoles, solo functions are normally routed to headphones (non-destructive solo), allowing the engineer to check console channels while the concert is in progress. In-place solo is a function that permits the user to hear individual channels but in the correct stereo perspective as defined by that channel's pan control.

S/PDIF: acronym for Sony/Philips Digital Interface, a "consumer" digital interface using either fiber-optic or coaxial (RCA) connections that allow the transfer of digital audio data from one device to another.

SPL: abbreviation for "sound pressure level," a means of expressing sound levels. Frequently used as a comparative measure of speaker efficiency or maximum system output.

THD: abbreviation for "total harmonic distortion," a condition where a circuit adds additional unwanted harmonics (e.g., second and third harmonics) that were not part of the original signal. THD represents the effect of all the harmonic components (hence, the "total" part of the name, as opposed to second- or fifth-harmonic distortion) and is usually expressed as a percentage of the signal.

TRS: abbreviation for "tip, ring, sleeve." A type of three-conductor ("stereo") connector used on some phone and TT connectors. The tip and ring carry the program signal and the sleeve is ground. TRS connectors are commonly used for stereo jacks (left, right, ground), console channel insert points (send, return, ground) and monaural balanced lines (in-phase, out-of-phase, ground). See balanced line.

TT CONNECTOR: Abbreviation for "Tiny Telephone," TT connectors use miniature phone plugs with a 0.173-inch diameter shaft. Due to their compactness and reliability, TTs are often used for professional console and outboard patchbays in studios and live sound applications, in which a single patchbay may require hundreds of patch points in a limited space. The TRS versions of TT connectors are capable of handling balanced line signals and are preferred in pro audio installations. See phone connector, patchbay, balanced line.

VCA: abbreviation for voltage-controlled amplifier, an amplifier circuit whose output gain can be varied by an external voltage.

VOLT: a unit of measure of electromotive force (resulting from a difference in electrical potential) equal to the force required to produce a current of one ampere through an element having a resistance of one ohm.

VOLTAGE-CONTROLLED AMPLIFIER: See VCA.

WATT: unit of measure of electrical power dissipation, formally defined as one joule (a unit of energy) per second, which is equal to the power absorbed by one ohm of resistance when one ampere of current is in the circuit. Electrical power, measured in watts, can be derived in three ways: the voltage squared divided by the resistance (V2/R), the current squared times the resistance (I2R) and the product of the voltage and the current (VI). Named for James Watt, inventor of the steam engine and the speed governor.

WHITE NOISE: a test signal comprising random noise, providing constant energy at all frequencies, similar to the sound heard when an FM radio is set between stations.

XLR: Developed by ITT/Cannon, XLRs are rugged, locking, multi-pin connectors frequently used in professional audio equipment. While 3-pin XLRs are most commonly seen on microphones and console inputs, other configurations also exist, such as 4-pin XLRs (a standard for stage intercom systems) and 5-pin XLRs (often used on stereo microphones).