Oct 27, 2004 5:16 PM

Active Crossover: A dividing network that splits a fullrange signal into two or more frequency groups and routes them to feed the various components (e.g., woofers and tweeters) in a speaker system. Active crossovers divide a line-level output signal from a mixer or other sound source and route the resulting signals to individual amplifiers that drive different speaker components. Passive crossovers usually are built inside speaker cabinets where they divide an amplifier's output signal for routing to different speaker combinations. See Bi-amp.

AES/EBU Digital Standard: digital audio standard developed 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.

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.

Amplitude: magnitude, or level, of an electrical signal (voltage) or acoustical signal (volume).

Attenuation: The process of decreasing a signal’s amplitude 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. See decibel, resistor.

Baffle: typically, a term referring to the board on which a speakers are mounted. Due to weakening of the board caused by mounting holes cut into it for speakers, ports, vents, etc., the front baffle of a cabinet is sometimes thicker than the other sides of an enclosure.

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 and 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 "uninverted" noise, it cancels it out. Balanced lines thus 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.

Bass Reflex: a popular enclosure design that uses a tuned port to extend a loudspeaker's bass response by allowing some of the air movement from a woofer cone's rear motion to combine with the bass frequencies from the cone's front movement. However, to avoid phase cancellation from occurring when these signals are combined, the port length and diameter must be carefully matched (tuned) to the speaker's free-air resonance and the enclosure volume.

Bi-Amp: short for "bi-amplification." A two-way audio system in which the signal is divided by frequency into two signals that are independently amplified and fed to separate speaker system components (e.g., woofers and tweeters). In a "tri-amped" system, signals are divided by frequency into three individually amplified groups. See crossover.

Bi-Wiring: a method of connecting speakers to amplifiers, whereby two sets of wires (one for highs, one for lows) run from the amp output to individual inputs on the speaker. Not to be confused with bi-amping, bi-wiring requires a speaker with separate inputs for the passive crossover in the low and high sections. (These can also be jumped together for "normal" connections.) The practice is far from universal and somewhat controversial, although fans of bi-wiring contend that a performance enhancement can be had by simply adding another set of speaker wires to a system.

Bridged Mono: a method of combining both channels of certain stereo power amplifiers to create a doubly powerful single-channel (monaural) amp. See monaural.

Capacitor: An electrical component with the ability to store an applied electrical charge, a capacitor is often used in crossovers as a means of blocking low frequencies from reaching midrange or tweeter components.

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

Compression Driver: a specialized mid- or high-frequency speaker comprising a small diaphragm and voice coil coupled to a large magnet structure. The unit is mounted to a horn, which acoustically matches the impedance of the driver to the impedance of the air and shapes the signal. Compression drivers tend to be expensive due to the precision tolerances required in their manufacture, but they deliver many times more sound-pressure-per-watt of input power than traditional direct-radiating cone speakers.

Crossover: a dividing network that splits a full-range signal into two or more frequency groups and routes them to feed the various components (e.g., woofers and tweeters) in a speaker system. Passive crossovers are usually built inside speaker cabinets where they divide an amplifier's output signal for routing to different speaker combinations. Active crossovers divide a line-level output signal from a mixer or other sound source and route the resulting signals to individual amplifiers that drive different speaker components. See bi-amp.

Cut-Off Frequency: the frequency point above or below that a filter strongly attenuates a signal. (Usually, the signal's output level at the cut-off frequency is 3 dB below its input level.) In a lowpass filter, a high cut-off frequency allows most of a sound through and generally produces a bright sound, while a low cut-off frequency blocks most of the sound and produces a muted or plain sound. See highpass filter, lowpass filter.

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. One 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.

Decibel: A unit of measure used to logarithmically express ratios of change in power or signal levels. A decibel is 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. In electronic music, audio signals, or the nuances of a performance (in the form of MIDI data), can be stored in digital form. The stored numbers can be translated back into sound or can reproduce the performance on electronic instruments.

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.

DIP Switch: A bbreviation for Dual In-line Package, this is one or a series of compact switches designed for mounting directly on a circuit board. DIP switches are often found inside computers and other electronic gear as a method of setting user preferences and defaults, usually in "set-and-forget" applications.

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.

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." See graphic equalizer, parametric equalizer.

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. Feedback also can be used in signal processing; for example, part of a signal routed through a digital delay can be fed back into the delay to create a more complex effect. This also is called "regeneration."

Filter: a device that attenuates or removes certain elements or data from an audio waveform or data stream. A MIDI data filter removes certain messages (pitch bend, program change, active sensing, etc.) from the MIDI data stream. See bandpass filter, band-reject filter, highpass filter, lowpass filter.

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

Fundamental Frequency: the lowest root frequency component of a periodic waveform. The fundamental frequency of a sound usually is perceived as its pitch. (Sometimes, this is true even when the fundamental's amplitude is lower than that of its harmonics.) See harmonics.

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

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

Ground Loop: a condition occurring 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.

I/O: abbreviation for "Input/Output."

Impedance: Measured in ohms, this is a way of expressing a circuit's opposition (resistance and reactance) to a signal or current attempting to pass through. The practical difference between impedance and resistance is that impedance changes as a function of frequency.

Infinite Baffle: alternative term for a sealed speaker enclosure. Because the sound waves created by a speaker cone's rear motion cannot interact with those emanating from the front of the cone, the effect of the sealed box is akin to having a front baffle of "infinite" size, hence the phrase "infinite baffle."

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."

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.

Lowpass Filter: a circuit designed to attenuate frequencies that occur above some designated point while allowing lower frequencies to pass unaffected.

Millisecond: one one-thousandth of a second. Abbreviated "ms."

Monaural: having one audio channel.

ms: See millisecond.

Near-Field Speaker: a compact studio monitor designed for listening at close distances, typically between three and five feet. When sitting at this near-field distance, the listener hears a greater proportion of direct sound from the monitors (compared to the reflected sound bouncing around the room) so, in theory, the effects of poor room acoustics are greatly reduced.

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.

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. See Q.

Passive Crossover: a dividing network that splits a full-range signal into two or more frequency groups and routes them to feed the various components (e.g., woofers and tweeters) in a speaker system. Passive crossovers usually are built inside speaker cabinets, where they divide an amplifier's output signal for routing to different speaker combinations. Active crossovers divide a line-level output signal from a mixer or other sound source and route the resulting signals to individual amplifiers that drive different speaker components.

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° (180° positive and 180° negative). Absolute phase is a reference point in time within one cycle—e.g., halfway through one period, the waveform's phase is 180°; at one-quarter of the waveform, the phase is 90°. 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° at its peak positive value) and the other is three-quarters of the way through its cycle (270° at its greatest negative value), they are 180° 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.

Phase Shift: a slight time difference between two similar waveforms, which puts them out-of-phase with respect to each other.

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, then 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 that are 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 are almost universally used for the outputs on phonographs.

Pink Noise: a test signal comprising random 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.

Psychoacoustics: the study of how sounds affect the human brain. During the years, psychoacoustic research has resulted in an improved understanding of human hearing, such as the way the brain processes sounds picked up by the left and right ears and translates subtle differences between the two into cues that indicate directionality.

Q: in filters, the ratio of a bandpass or band-reject filter's center frequency to its bandwidth. Thus, assuming a constant center frequency, Q is inversely proportional to bandwidth (i.e., higher Q values indicate a narrower bandwidth). For this reason, the term is often used to denote bandwidth. See parametric equalizer, resonance.

RCA Connector: See phono connector.

Resistor: an electronic component that opposes the flow of electrical current. Resistance is measured in ohms (?).

Resonance: the property possessed by a simple vibrating body of oscillating more strongly in sympathy with a regular oscillatory disturbance at the same frequency. When a vibrating object (such as a guitar body) is stimulated by a second oscillator (such as a vibrating string), its pattern of vibration may be altered. If the two vibrate at the same (or a harmonically related) frequency, they tend to phase-lock together in sympathetic vibration at this common resonant frequency. The amplitude of their vibration is thus greatly increased. Oscillations at nonharmonic frequencies have far less effect. The same principle holds with electrical signals.

Reverberation: the decaying residual signal that remains after a sound occurs, created by multiple reflections as the original sound wave bounces off walls, furniture and other barriers within a room or other acoustical environment. Modern reverb effects processors use digital signal processing (DSP) techniques to simulate acoustical spaces. Analog methods of simulating reverberation include spring reverbs (commonly used in guitar amps), plate reverbs (which use a mechanical transducer to vibrate a large metal plate) and reverb chambers (where signals from a speaker sounding in a room are picked up by one or more microphones).

RMS: abbreviation for Root-Mean-Square, a formula to describe the level of a signal. RMS is derived by squaring all the instantaneous voltages along a waveform, averaging the squared values and then taking the square root of that number. When used to describe power amplifiers, RMS power (in watts) is considered a more useful measure of power output than "program" or "peak" power. (A power amp's performance depends on the nature of the input signal. "Peak" power ratings don't account for this, whereas RMS ratings, because they are derived from multiple points in a sine wave, more closely reflect the actual energy content of the input signal.) RMS also is used to measure input sensitivity (in volts) in a preamp or line amplifier.

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.

Sensitivity: a measure of the relative efficiency of a speaker or loudspeaker system, often expressed as the number of decibels the unit will produce fed from a 1-watt signal measured at a distance of one meter.

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.

Sine Wave: a continuous periodic waveform whose amplitude varies as the sine of the linear function of time. Occasionally referred to as a sinusoidal wave, it has no harmonics except the fundamental.

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. SPL is frequently used as a comparative measure of speaker efficiency or maximum system output.

THD: abbreviation for "Total Harmonic Distortion," a condition in which 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." TRS is a type of 3-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.

Transducer: a device that transforms energy from one form to another. Examples of electromechanical transducers include microphones (which convert acoustic pressure into electrical voltage) and loudspeakers (which convert voltages into acoustic pressure).

Translation: the ability of mixes created on one set of monitors to playback consistently ("translate") to other systems.

Tweeter: a loudspeaker designed to produce high frequencies.

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.

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). Watt is named for James Watt, inventor of the steam engine.

Waveform: a 2-D graph of one period of a signal, showing changes in pressure (amplitude) as a function of time.

Wavelength: the distance from the beginning to the end of one cycle (or from equivalent points in two consecutive cycles) of a waveform. A wavelength is equal to the speed of sound times the frequency of the waveform.

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.

Woofer: a speaker designed to reproduce low frequencies.

XLR: Developed by ITT/Cannon, XLRs are rugged, locking multipin 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).