Digital music, indeed most computer stuff these days, attracts it's share of abbreviations and acronyms... so many in fact that, as much as I've tried to make this site accessible to all users - including speech-enabled browsers - this area is the most time-consuming to code.

Therefore, these glossary pages are the best place for "decrypting".

Music glossary pages:

Digital Audio Glossary: A-G

Jump to:

A-B Test

A test between two components. For example, a test between two different pre-amplifiers, or, when mixing, a test between a song with EQ tweaks, against the same song without.

For the test to be scientifically valid the levels should be matched.

ABX Comparator

A device that randomly selects between two components being tested. The listener doesn't know which device is being listened to.


See Dolby Digital

Acoustic suspension

A sealed or closed box speaker enclosure.


Balanced digital connection. For example, used to connect a CD transport to a DAC. The AES/EBU standard uses XLR type connectors.


A class of enclosure parameters that provides optimum performance for a woofer with a given value of Q.


Term used in sealed enclosure designs to mean the ratio of Vas to Vb, where Vb is the volume of the box you will build.

Alternating Current (AC)

An electrical current that periodically changes in magnitude and direction.


The acoustic characteristics of a space with regard to reverberation. A room with a lot of reverb is said to be "live"; one without much reverb is "dead."

Ampere (A)

The unit of measurement for electrical current in coulombs per second. There is one ampere in a circuit that has one ohm resistance when one volt is applied to the circuit. See Ohms Law.

Amplifier (Amp)

A device which increases signal level. Many types of amplifiers are used in audio systems. Amplifiers typically increase voltage, current or both.

Amplifier classes

Audio power amplifiers are classified primarily by the design of the output stage. Classification is based on the amount of time the output devices operate during each cycle of signal swing. Also defined in terms of output bias current, (the amount of current flowing in the output devices with no signal).

  • Class A: Operation is where both devices conduct continuously for the entire cycle of signal swing, or the bias current flows in the output devices at all times. The key ingredient of class A operation is that both devices are always on. There is no condition where one or the other is turned off. Because of this, class A amplifiers are single-ended designs with only one type polarity output devices. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, class A amplifiers are large, heavy and run very hot. All this is due to the amplifier constantly operating at full power.The positive effect of all this is that class A designs are inherently the most linear, with the least amount of distortion.
  • Class B: Operation is the opposite of class A. Both output devices are never allowed to be on at the same time, or the bias is set so that current flow in a specific output device is zero when not stimulated with an input signal, i.e., the current in a specific output flows for one half cycle. Thus each output device is on for exactly one half of a complete sinusoidal signal cycle. Due to this operation, class B designs show high efficiency but poor linearity around the crossover region. This is due to the time it takes to turn one device off and the other device on, which translates into extreme crossover distortion. Thus restricting class B designs to power consumption critical applications, e.g., battery operated equipment, such as 2-way radio and other communications audio.
  • Class AB: Operation allows both devices to be on at the same time (like in class A), but just barely. The output bias is set so that current flows in a specific output device appreciably more than a half cycle but less than the entire cycle. That is, only a small amount of current is allowed to flow through both devices, unlike the complete load current of class A designs, but enough to keep each device operating so they respond instantly to input voltage demands. Thus the inherent non-linearity of class B designs is eliminated, without the gross inefficiencies of the class A design. It is this combination of good efficiency (around 50%) with excellent linearity that makes class AB the most popular audio amplifier design.
  • Class AB plus B: Design involves two pairs of output devices: one pair operates class AB while the other (slave) pair operates class B.

  • Class D: Operation is switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle. Since the output devices are either completely on or completely off they do not theoretically dissipate any power. Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product we're still waiting for; meanwhile designs do exist with true efficiencies approaching 90%.
  • Class G: Operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single class AB output stage that is connected to two power supply rails by a diode, or a transistor switch. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks. Another approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs.
  • Class H: Operation takes the class G design one step further and actually modulates the higher power supply voltage by the input signal. This allows the power supply to track the audio input and provide just enough voltage for optimum operation of the output devices. The efficiency of class H is comparable to class G designs.


To reduce in level.


Before digital, the way all sound was reproduced. A smooth wavecycle rather than the digital 1's and 0's.

A better comparison is described in TheWhippinpost's audio and MIDI latency article.


Refers to a type of bass-cabinet loading. An aperiodic enclosure type usually features a very restrictive, (damped), port. The purpose of this restrictive port is not to extend bass response, but lower the Q of the system and reduce the impedance peak at resonance. Most restrictive ports are heavily stuffed with fiberglass, dacron or foam. 


A person interested in sound reproduction.


Adaptive Woofer System, trademark of ACI. An active woofer system with built in user adjustable equalization capabilities.



  A surface used to mount a loudspeaker.


Referring to wiring: Audio signals require two wires. In an unbalanced line the shield is one of those wires. In a balanced line, there are two wires plus the shield. For the system to be balanced requires balanced electronics and usually employs XLR connectors. Balanced lines are less apt to pick up external noise. This is usually not a factor in home audio, but is a factor in professional audio requiring hundreds or even thousands of feet of cabling. Many higher quality home audio cables terminated with RCA jacks are balanced designs using two conductors and a shield instead of one conductor plus shield.


The total frequency range of any system. Usually specified as something like: 20-20,000Hz plus or minus 3 db.

Band-pass Enclosure

A multi-chambered ported system.

Band-pass filter

An electric circuit designed to pass only middle frequencies.

Bass Blockers

Commercial name for auto-sound first order high pass crossovers (non-polarized capacitors), generally used on midbass or dash speakers to keep them from trying to reproduce deep bass.

Bass Reflex

A type of loudspeaker that uses a port or duct to augment the low-frequency response. Opinions vary widely over the "best" type of bass cabinet, but much has to do with how well a given design, such as a bass reflex is implemented.  


  A tendency of a loudspeaker to concentrate the sound in a narrow path instead of spreading it.

Bessel crossover

A type of crossover design characterized by having a linear or maximally flat phase response.  Linear phase response results in constant time-delay (all frequencies within the passband are delayed the same amount). Consequently the value of linear phase is it reproduces a near-perfect step response with no overshoot or ringing. The downside of the Bessel  is a slow roll-off rate. The same circuit complexity in a Butterworth response rolls off much faster.


The use of two amplifiers, one for the lows, one for the highs in a speaker system. Could be built into the speaker design or accomplished with the use of external amplifiers and electronic crossovers.


The use of two pairs of speaker wire from the same amplifier to separate bass and treble inputs on the speaker.


A type of connection often used in instrumentation and sometimes in digital audio. BNC connectors sometimes are used for digital connections such as from a CD Transport to the input of a DAC.


Listening term, refers to an excessive bass response that has a peak(s) in it.


Listening term. Usually refers to too much upper frequency energy.


Combining both left and right stereo channels on an automotive amplifier into one higher powered mono channel. When an amplifier is bridged, the impedance that the amplifier actually "sees" is calculated based upon the output of both stereo channels. Here is a simple formula to help define this:

Bridged Mono Impedance = (Y / X)/2

Y = impedance of driver(s) (both drivers should be identical)

X = # of drivers in circuit

One 4 ohm sub in bridged mono is equal to hooking up two 2 ohm subs in stereo, one to each channel.

Butterworth crossover

A type of crossover circuit design having a maximally flat magnitude response, i.e., no amplitude ripple in the passband. This circuit is based upon Butterworth functions, also know as Butterworth polynomials.


Cabin gain

The low frequency boost normally obtained inside a vehicle interior when subs are properly mounted.


A device made up of two metallic plates separated by a dielectric (insulating material). Used to store electrical energy in the electrostatic field between the plates. It produces an impedance to an AC current (Alternating Current).

CENTRE Channel (or center (US))

In home theater, sound decoded from the stereo signal sent to a speaker mounted in front of the listener, specially designed to enhance voices and sound effects from a movie soundtrack. Used in car audio to help offset skewed stereo imaging due to seating positions in the automotive environment.

Channel Balance

In a stereo system, the level balance between left and right channels. Properly balanced, the image should be centered between the left-right speakers. In a home-theater system, refers to achieving correct balance between all the channels of the system.

Chorus (Refrain)

A musical phrase normally based on a single-note melody line. A key component of an arrangement, it is a song's central motif that ups its recognition factor.


Refers to a type of distortion that occurs when an amplifier is driven into an overload condition. Usually the "clipped" waveform contains an excess of high-frequency energy. The sound becomes hard and edgy. Hard clipping is the most frequent cause of "burned out" tweeters. Even a low-powered amplifier or receiver driven into clipping can damage tweeters which would otherwise last virtually forever.

Class A, Class A-B etc...

In a sense, amplifying the audio signal means using the wall-current (usually either 120 or 240 volts) to increase the amplitude of the audio signal from mill-watts to watts. Different classes of amplifiers accomplish this in different ways. Turning a vacuum tube "on" or "off" with current demand increases the efficiency of the amplifier but may add switching distortion. A Class A amplifier is relatively inefficient, converting much energy to heat, but has no switching distortion.


Mechanical suspension compliance of a driver, consisting of the spider and surround.


A speaker type that utilizes a tweeter mounted at the center of a woofer cone. The idea being to have the sound source through the full frequency range become "coincident". 

Coaxial Driver

- a speaker composed of two individual voice coils and cones; used for reproduction of sounds in two segments of the sound spectrum. See also triaxial driver.


Listening term. Refers to how well integrated the sound of the system is.


Listening term. A visual analog. A "colored" sound characteristic adds something not in the original sound. The coloration may be euphonically pleasant, but it is not as accurate as the original signal.


  The relative stiffness of a speaker suspension, specified as Vas.


In audio, compression means to reduce the dynamic range of a signal. Compression may be intentional or one of the effects of a system that is driven to overload.

Compression tutorial


A frequency divider. Crossovers are used in speakers to route the various frequency ranges to the appropriate drivers. Additionally, many crossovers contain various filters to stabilize the impedance load of the speaker and or shape the frequency response. Some crossovers contain levels controls to attenuate various parts of the signal.

A passive crossover uses capacitors, coils and resistors, usually at speaker level. A passive crossover is load dependent (the transition may not be very smooth or accurate if a different speaker is substituted for the one the crossover was designed for).

An active crossover is based on integrated circuits (ICs), discreet transistors or tubes. An active crossover is impedance buffered and gives a consistent and accurate transition regardless of load.

Crossover Slope

High and low pass filters used for speakers do not cut-off frequencies like brick walls. The rolloff occurs over a number of octaves. Common filter slopes for speakers are 1st through 4th order corresponding to 6db/oct to 24db/oct. For example, a 1st. order, 6db/oct high pass filter at 100hz will pass 6db less energy at 50Hz and 12db less energy at 25Hz. Within the common 1st through 4th filters there is an endless variety of types including Butterworth, Linkwitz-Riley, Bessel, Chebychev, etc. Salesmen and product literature will sometimes make claims of clear superiority for the filter used in the product they are trying to sell. Since the subject fills books, suffice it to say that there is no one best filter, it depends on application and intended outcome. Good designers use the filters required to get the optimum performance from the system.


Unwanted breakthrough of one channel into another. Also refers to the distortion that occurs when some signal from a music source that you are not listening to leaks into the circuit of the source that you are listening to.


The process of removing unnecessary or undesirable sections of an audio or MIDI recording.



A Digital to Audio Converter. Converts a digital bitstream to an analog signal. Can be a separate "box" that connects between a CD Transport or CD Player and a pre-amplifier.

Damping (Damping factor)

Refers to the ability of an audio component to "stop" after the signal ends. For example, if a drum is struck with a mallet, the sound will reach a peak level and then decay in a certain amount of time to no sound. An audio component that allows the decay to drag on too long has poor damping, and less definition than it should. An audio component that is overdamped does not allow the initial energy to reach the full peak and cuts the decay short. "Boomy" or "muddy" sound is often the result of underdamped systems. "Dry" or "lifeless" sound may be the result of an overdamped system.


Joe D'Appolito is credited with popularizing the MTM (Midrange-Tweeter-Midrange) type of speaker.

Decibel (dB)

Named after Alexander Graham Bell. We perceive differences in volume level in a logarithmic manner. Our ears become less sensitive to sound as its intensity increases. Decibels are a logarithmic scale of relative loudness. A difference of approx. 1 dB is the minimum perceptible change in volume, 3 dB is a moderate change in volume, and about 10 dB is an apparent doubling of volume:

  • 0 dB is the threshold of hearing, 130 dB is the threshold of pain.
  • Whisper: 15-25 dB
  • Quiet background: about 35 dB
  • Normal home or office background: 40-60 dB
  • Normal speaking voice: 65-70 dB
  • Orchestral climax: 105 dB
  • Live Rock music: 120 dB+
  • Jet aircraft: 140-180 dB


A process by which data on a hard disk is rearranged in an order that enhances performance. Special defragmenting utilities are available for Windows and Mac OS.

Optimise your PC for audio


The part of a dynamic loudspeaker attached to the voice coil that moves and produces the sound. It usually has the shape of a cone or dome.


A change in the direction of a wave front that is caused by the wave moving past an obstacle.


An open-back speaker that radiates sound equally front and rear. The front and rear waves are out of phase and cancellation will occur when the wavelengths are long enough to "wrap around". The answer is a large, wide baffle or to enclose the driver creating a monopole.

Direct Current (DC)

Current that moves in only one direction.


The spreading of sound waves as they leave a source. The spreading of sound waves as they leave a source.


Anything that alters the musical signal. There are many forms of distortion, some of which are more audible than others. Distortion specs are often given for electronic equipment which are quite meaningless. As in all specifications, unless you have a thorough understanding of the whole situation, you will not be able to make conclusions about the sonic consequences.


Abbreviation for Do- It-Yourself. In audio, the most common DIY is building speakers but some hobbyists build everything from pre-amps to amplifiers to DACs.

Dolby Digital

Five-channel system consisting of left, center, right and left rear, right rear channels. All processing is done in the digital domain.

Unlike Dolby Prologic in which the rear effects channels are frequency limited to approx. 100-7000Hz, Dolby Digital rear channels are specified to contain the full 20-20Khz frequency content.

The AC3 standard also has a separate subwoofer channel for the lowest frequencies.

Dolby Digital EX Surround

Also referred to as Dolby Digital 6.1, adds a rear, center channel to the existing left, center, right and rear speakers. This format requires a 6.1 processor or receiver and DVDs that are 6.1 encoded.

Dolby Prologic

Four-channel system consisting of left, center, right and rear channel, (the single rear channel is usually played through two speakers).

Dome Tweeter

A high frequency speaker with a dome-shaped diaphragm.A high frequency speaker with a dome-shaped diaphragm.

Double (Dual) Voice Coil (DVC)

A voice coil with two windings, generally used in woofers. Each voice coil can be connected to a stereo channel, or both voice coils can be wired in parallel or series to a single channel.


Digital Theater System. A multi-channel encoding/decoding system. Used in some movie theaters. Also now included in some home-theater processors. A competitor to Dolby Digital.


Digital Signal Processing. DSP can be used to create equalization, compression, etc. of a digital signal.


Digital Video Disc or Digital Versatile Disc. A relatively new standard that seeks to combine better-than-laser-disc quality video with better-than-CD quality audio in a disc the size of a CD. Requires special players. Seems to be a viable candidate to replace both Laser Discs and CDs, but the jury is still out.

Dynamic Headroom

The ability of an audio device to respond to musical peaks. For example, an amplifier may only be capable of a sustained 100 watts, but may be able to achieve peaks of 200 watts for the fraction of a second required for an intense, quick sound. In this example the dynamic headroom would equal 3 db.

Dynamic range

The range between the loudest and the softest sounds that are in a piece of music, or that can be reproduced by a piece of audio equipment without distortion (a ratio expressed in decibels). In speech, the range rarely exceeds 40 dB; in music, it is greatest in orchestral works, where the range may be as much as 75 dB.



Efficiency Bandwidth Product.

A guide that helps a designer determine whether a driver is more suitable for a sealed or ported enclosure.

EBP of less than 50 indicates the driver should be used in a sealed enclosure. 50 - 90 indicates flexible design options... over 90 indicates best for a ported enclosure.

EBP = Fs / Qes


Processing windows in which MIDI and audio tracks are processed or edited in detail.

MIDI editors


Devices or plug-ins that refine or reshape audio signals. Reverb, delay and chorus are typical effects that see widespread use.

Efficiency rating

The loudspeaker parameter that gives the level of sound output when measured at a prescribed distance with a standard level of electrical energy fed into the speaker.

Electronic Crossover

Uses active circuitry to send signals to appropriate drivers. More efficient than passive crossovers. Uses active circuitry to send signals to appropriate drivers. More efficient than passive crossovers.

Electrostatic Speaker

A speaker that radiates sound from a large diaphragm that is suspended between high-voltage grids.

Enhanced IDE (Integrated Device Electronics)

This standard serves to connect hard disks and other mass storage media to a computer.


Electronic set of filters used to boost or attenuate certain frequencies.

Equaliser in Cubase tutorial


How extended a range of frequencies the device can reproduce accurately. Bass extension refers to how low a frequency tone will the system reproduce, high-frequency extension refers to how high in frequency will the system play.


Fc or Fcb

The system resonance frequency of a driver in a sealed box. The system resonance frequency of a driver in a sealed box.


An electrical circuit or mechanical device that removes or attenuates energy at certain frequencies. .

Flat Response

The faithful reproduction of an audio signal; specifically, the variations in output level of less than 1 dB above or below a median level over the audio spectrum.


The roll-off frequency at which the driver's response is down -3dB from the level of it's midband response. 

Fletcher-Munson curve

Our sensitivity to sound depends on its frequency and volume. Human ears are most sensitive to sounds in the midrange. At lower volume levels humans are less sensitive to sounds away from the midrange, bass and treble sounds "seem" reduced in intensity at lower listening levels.

Free Air Resonance

The natural resonant frequency of a driver when operating outside an enclosure. 


The range of human hearing is commonly given as 20-20,000Hz (20Hz-20kHz). One hertz (Hz) represents one cycle per second, 20Hz represents 20 cycles per second and so on. Lower numbers are lower frequencies


The frequency of resonance for a driver in free air. 


A speaker designed to reproduce all or most of the sound spectrum. 


The lowest frequency of a note in a complex wave form or chord.  



To increase in level. The function of a volume control.


Found on many PC audio cards, it is a connector designed to take joysticks. With a MIDI adapter, it can be used as a simple MIDI interface.