Glossary of Terms

At Sight+Sound Gallery we want to empower you with all of the information you need to make informed decisions when purchasing your audio, video, and home automation equipment. Of course, we are here to personally answer your questions. Call, email or or use our website's chat functionality if you want to talk to us directly. If however you want to do some research on your own, this Glossary offers useful definitions of many of the terms you will see on our website.

Absorption – In acoustics, the tendency of certain materials to absorb (as opposed to reflect) sound waves. A material's absorption coefficient is a value between 0 (total reflection) and 1 (total absorption), which varies according to the sound's frequency and angle of incidence.

Acoustic Suspension - A type of speaker enclosure that uses a sealed box to provide tight, accurate bass response. It gives up some efficiency to provide bass that is typically more accurate and controlled than that of a ported bass reflex design. Acoustic suspension speakers may require more amplifier power than than a bass reflex speaker to play at the same volume level.

A/D converter (ADC) -Analog-to-digital converters are devices that transform incoming analog signals into digital form.

Aliasing -This is a type of distortion caused during the analog-to-digital conversion process. If the frequency of the analog signal exceeds one-half the sampling rate, spurious signals and harmonics not present on the original signal may be created.

Ambiance - The feeling or mood evoked by an environment. The acoustic qualities of a listening space, including the background noise and perceived sense of space. Adding echo or reverb to music can enhance its ambience, giving listeners a sense of what kind of room it's being played in.

Ambience - The aurally perceived impression of an acoustical space, such as the performing hall in which a recording was made.

Amperage - A measure of electrical current. An ampere — often referred to as an amp — is the unit of measure for the rate of current flow past a certain point and in a given amount of time, through an electrical conductor. Using water flow as a metaphor, amperage would represent the water volume, while voltage represents water pressure.

Amplifier - An electrical circuit designed to increase the current or voltage of an applied signal.

Amplitude - The relative magnitude of a signal.

Analog - An analog is a representation of something. Analog audio signals use changes in voltage to represent changes in sound pressure. On vinyl records, groove depth is an analog for sound pressure levels. On analog tape, changes in magnetism are an analog for changes in sound pressure. This continuous representation of sound is a key difference between analog and digital systems, which use “quantized,” or sampled representation.

Attenuation - The reduction of an electrical signal. To reduce or make quieter.

Auxiliary -In sound mixers, supplemental equipment or features that provide additional capabilities to the basic system. Examples of auxiliary equipment include: serial processors (equalizers, compressors, limiters, gates) and parallel processors (reverberation and delay).

Audio Frequency - The acoustic spectrum of human hearing, generally regarded to be between 20 Hz and 20 kHz.

Baffle - A board or other planar surface used to mount a loudspeaker.

Bandwidth - The range of frequencies reproduced by an amplifier or transducer.

Balance- 1) The subjective relationship between the relative loudness of the upper and lower halves of the audio spectrum; "tonal balance." 2) The relative loudness of the instruments in a performing group. 3) Equality of signal level between the left and right stereo channels, which centers the soundstage and allows mono program material to image at the center. Also called channel balance.

Banana Plug - A connector designed primarily for connecting speaker wire to the binding posts on the back of power amplifiers and speakers.

Bandwidth - The range of frequencies that can be produced – or reproduced – by a transmission medium or piece of equipment. The bandwidth of human hearing is generally considered to be 20 Hz to 20,000 Hz, although there are harmonic components in audio that extend above 20,000 Hz.

Bass -The low end of the audio frequency spectrum between 0Hz to about 200 Hz.

Bass Reflex - A type of speaker enclosure that includes a "tuned" port or passive radiator to increase and extend bass response (by releasing some of the energy created by the inward movement of the woofer cone). Bass reflex designs are more power-efficient than acoustic suspensions designs — they'll play louder when driven with the same amplifier power. But they may sacrifice some bass accuracy in exchange for the added bass output.

Bi-Amping and Bi-Wiring - Some higher performance speakers include dual sets of connectors, usually the type known as "binding posts," Models with dual connectors almost always also feature a special type of crossover with separate "high-pass" and "low-pass" sections. These connectors may also be shunted together with jumpers to accommodate conventional hook-ups.

Binaural - Literally hearing with "two ears". Refers to a recording/playback system that presents the listener's ears with the acoustic waveforms they would have received at the original event.

Bit Depth- Describes the number of bits a digital device uses to process audio. Bit depth refers to the dynamic range that can be captured during recording. The number of possible "levels" that can be recorded at 16-bit is 65,536 (2 to the 16^th power), while this figure jumps to 16,777,216 using 24-bit hardware.

Bunching - 1) In double-mono reproduction, the imaging of all sounds from a small area between the loudspeakers. Tight (narrow) bunching in A+B mode is essential for good imaging specificity in stereo. 2) In stereo reproduction, excessive center fill will result in inadequate spread.

Bus - In audio, a bus is a point in a circuit where many signals are brought together. For example, a mixer assigns input signals to a bus, and the bus carries all the signals, mixed together, to an output. There's a left main output bus, and a right main output bus. There may also be an auxiliary bus, a monitor bus, or an effects bus that carry these designated mixes to where they need to go. The more buses a mixer has, the more flexible its routing and control capabilities will be.

Cardioid - A microphone pickup pattern with strong sensitivity to sound presented to the front of the microphone, good but reduced sensitivity to sources on the sides, and good rejection of sound coming from the rear. Cardioid mics are popular for both studio and live use.

Circuit - A complete path that allows electrical current from one terminal of a voltage source to the other terminal.

Class A - A “Class A” transistor amplifier conducts for the entire cycle of input signal, conduction angle 360 deg. Runs hot, as the transistors in the power amp are on all the time, but has high sound quality. A type of amplifier circuit where the output device is always on for both parts of a complete audio waveform. Class A amplifiers are large, heavy, inefficient, and run very hot, due to the amplifier constantly operating at full power. Class A amps produce very low distortion and are mostly found in high-end equipment.

Class B -In a “Class B” amplifier, positive and negative halves of the signal are dealt with by different parts of the circuit, the output devices switching continually. A Class B amplifier circuit differs from Class A in that there is no current flowing when the output devices are at idle, and as a result, they have to turn on from a zero current state when signal is present. Class B amps tend to have more crossover distortion than Class A amps but are less costly to build because they can use less robust power supplies.

Class AB -A “Class AB” transistor amplifier produces a non-zero DC current much smaller than the peek current of the signal source. A second transistor conducts during the negative half cycle of the waveform and the currents from the 2 transistors are combined at the load. A compromise between sound quality of Class A and efficiency of Class B, most amp designs employ this method. A type of amplifier circuit that combines aspects of both Class A and Class B operation. If an amplifier operates in Class A for only a portion of its output, and has to turn on additional current in the devices for the remainder of its output, it is operating in Class AB.

Clipping - A form of distortion caused by cutting off the peaks of audio signals. Clipping usually occurs in the amplifier when it's input signal is too large or when the voltage rails of the power supply cannot deliver the necessary voltage to the power amp. Clipping occurs in analog and digital audio circuits when the incoming signal exceeds what a particular device can accommodate. Viewed on an oscilloscope, it results in the flattening of the signal peaks, as if the waveform had been "clipped" off. In certain analog circuits light clipping can have a positive effect, producing a pleasing distortion. In digital circuits the general rule is that clipping is to be avoided at all costs, since it produces an unpleasantly harsh sound.

Codec - Short for encoder/decoder. A piece of hardware or software capable of encoding or decoding a digital data stream. In audio, there are "lossy" codecs like MP3 that discard some of the information in the original file. There are also lossless codecs like FLAC, which provide bit-perfect accuracy in a file that is significantly smaller than the original.

Coloration - Any change in the characteristic of sound that reduces naturalness, such as an overemphasis of certain tones. – or - An audible "signature" with which a reproducing system imbues all signals passing through it.

Comb Filter - A distortion produced by combining an electronic or acoustic signal with a delayed copy of itself. The result is peaks and dips introduced into the frequency response.

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

Compression Driver - A compression driver is a high frequency speaker or tweeter designed to mount at the rear of an acoustic horn, which amplifies the sound and improves the speaker's efficiency. The driver's sound compresses in the horn's throat and expands with its outward flare.

Compressor - A circuit that performs dynamic compression of an audio signal. By setting the ratio and threshold controls, it's possible to level out large dynamic swings. For instance, a 2:1 ratio means that if the program material rises by two decibels, the output will only rise by one decibel, once the threshold setting has been exceeded.

Condenser Microphone - Type of microphone in which the capsule consists of conductive diaphragm next to a backplate. Condenser mics need power, which can be provided by batteries or a phantom power supply in the mixer. Applying an electric charge basically creates a capacitor out of the capsule. Sound waves hitting the diaphragm cause it to move in relation to the backplate, producing a variation in the capacitance of the capsule. This in turn produces a variance in the output voltage, which can then be turned back into acoustic energy.

Cone - The conical diaphragm of a speaker attached to the voice coil that produces pulsation's of air that the ear detects as sound.

Crossover – An electrical device that divides the audio spectrum of an audio signal into smaller groups of frequencies, making it easier for downstream components to handle the load. The most common use of crossovers is in amplifier/speaker systems, which allows the separate components to function more accurately and efficiently.

Crossover Frequency – The frequency at which the driver's roll off at - usually when response is down -3dB. See Roll-off.

Crossover Network (Filter) – An electric circuit or network that splits the audio frequencies into different bands for application to individual speakers. See Electronic and Passive Crossover.

Current –The flow of electrical charge measured in amperes.

D/A Converter (DAC) - A digital-to-analog converter takes a digital audio bitstream containing ones and zeros and reconstructs it back into an analog waveform. DACs come in a variety of configurations and prices ranges, and vary in how accurately they can reassemble the program material.

Damping -The reduction of movement of a speaker cone, due either to the electromechanical characteristics of the speaker driver and suspension, the effects of frictional losses inside a speaker enclosure, and/or by electrical means. – or – The amount of control an amplifier seems to impose on a woofer. Under damping causes loose, heavy bass; over damping yields very tight but lean bass.

Damping Factor - A power amplifier specification describing the amp’s ability to control speaker motion once signal has stopped. The effects of damping are most audible at low frequencies. An amplifier with a high damping factor will make a speaker sound "tighter" in the low end.

Data Compression – The process of making a digital audio or video stream more efficient for storage or transmission by using an algorithm that selectively eliminates bits of data. Examples of audio codecs that use data compression include MP3 and Dolby® Digital.

Decay -The reverberant fadeout of a musical sound after it has ceased. The time it takes for a signal to fall below audibility.

Definition -That quality of sound reproduction that enables the listener to distinguish between, and follow the melodic lines of, the individual voices or instruments comprising a large performing group.

Decibel (dB) – A logarithmic scale used to denote a change in the relative strength of an electric signal or acoustic wave. It is a standard unit for expressing the ratio between power and power level.

Detail – The subtlest, most delicate parts of the original sound, which are usually the first things lost by imperfect components.

Diaphragm – 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. The part of a microphone that is mechanically moved by sound waves. The resulting interaction with a backplate or moving coil (depending on the microphone type) allows the conversion of sound energy to electrical energy.

Diffraction - A change in the direction of a wave that is caused by the wave moving past or hitting an obstacle.

Diffuse –Reproduction that is severely deficient in detail and imaging specificity; confused, muddled.

Dispersion – The spreading of sound waves as it leaves a speaker.

Distortion – Any undesirable change or error in the reproduction of sound that alters the original signal. Any change in the shape of an audio waveform compared between two points in a signal chain. Generally the term refers to the desirable or undesirable "breaking-up" of audio

Dome Tweeter – A high frequency speaker driver with a dome-shaped diaphragm usually made of metal or silk.

Driver – A loudspeaker unit, consisting of the electromagnetic components of a speaker, typically a magnet and voice coil.

DSP (Digital Signal Processing) –Any form of manipulation performed on an audio signal while it is in digital form.

Dynamic Range – The range of sound intensity a system can reproduce without compressing or distorting the signal. Pertaining to a signal: the ratio between the loudest and the quietest passages. Pertaining to a component: the ratio between its no-signal noise and the loudest peak it will pass without distortion.

Echo– In an acoustical space: the repetition of a sound due to reflection of the original sound from a room boundary.

EMI (Electro Magnetic Interference) – Audible interference produced when equipment or cabling picks up stray electromagnetic fields. This interference may be heard as hum, static, or buzz. Sources of EMI include fluorescent lights, power lines, computers, TVs, lighting dimmers, and radio and TV transmitters.

Equalizer – Hardware device or computer plug-in used to alter the frequency balance of an audio source. An equalizer has the ability to boost or cut specific frequency ranges based around a center frequency. Equalizers come in various forms, including parametric and graphic, active or passive.

Extension –The usable limits of a component's frequency range.

Fader – A type of volume or level control typically found on mixing boards and graphic equalizers. A fader works like a standard potentiometer, only instead of rotating, it slides along a straight path.

Feedback – When a portion of the output signal is intentionally or unintentionally "fed back" into a device's input. One of the most common forms of feedback is the acoustic feedback that occurs when the sound from a loudspeaker gets picked by the microphone creating the sound, resulting in a squealing or ringing noise.

Filter - An electronic circuit designed to attenuate a sound source's energy at a particular frequency. Filters can be active or passive. Most filters these days are active, with amplifiers attached to them to allow the user to both boost and cut particular frequencies.

Flanging - An audio process where two copies of the same signal are played together, with one variably delayed against the other. Originally created by holding a finger against a tape flange (the metal part that holds the tape on the reel). Today, the effect is produced using digital effect processors.

Frequency Range –A range of frequencies stated without level limits: ie, "The upper bass covers the frequency range 80-160Hz."

Frequency Response – 1) A range of frequencies stated with level limits: ie, "The woofer's response was 20-160Hz ±3dB." 2) The uniformity with which a system or individual component sounds as if it reproduces the range of audible frequencies. Equal input levels at all frequencies should be reproduced by a system with subjectively equal output. In audio the indication of how many cycles of a repetitive waveform occurs during one second. A waveform which repeats once per second has a frequency of 1Hz. When applied to human hearing, frequency is often referred to as pitch.

Gain - The extent to which a circuit amplifies a signal. Usually part of an amplifier specification, its value is most often expressed in decibels.

Gain Staging - Setting the gain of each stage in the signal path so that one stage doesn't overload the next one in line.

Gain Structure – When multiple audio devices are used together, the gain structure of the system becomes an important consideration for overall sound quality. You have to look at which pieces are amplifying or reducing the signal, and by how much. A properly set up gain structure takes maximum advantage of the dynamic range and signal-to-noise ratio of each piece in the chain.

Gate (aka Noise Gate) – A dynamic device that has the ability to stop audio passing through it based on a certain threshold. Often called a "noise gate."

Graphic Equalizer – A type of equalizer that uses a series of slider controls to adjust the frequency bands, and the configuration of the sliders provide a "graphic" visual display of the EQ settings.

Ground – The common reference point for an electrical circuit, at zero voltage potential, that also represents the path for the electric charge to return to the power source.

Ground Lift Switch – A switch found on some equipment that disconnects the shield of a balanced cable from the local equipment ground. Used in situations where ground loops are a problem.

Ground Loop – A common problem that occurs when an audio system has multiple paths and path lengths to ground. Ground loops will cause varying levels of hum, occurring at 60 Hz or some multiple of 60 Hz because that is the line frequency of AC power in the U.S. You can sometimes cure ground loops through the use of ground lift switches, but generally it is better to find the offending piece of equipment and troubleshoot it to find the reason for the ground hum.

Haas Effect – A psychoacoustic effect where any delay signal below 40 milliseconds is indistinguishable from the source event. In other words, instead of hearing the sound and then a delay (two events), you hear both the source and the delay together as a single event. The effect is also called the precedence effect, meaning that if there are two sources of sound, as is often the case with PA systems or studio monitoring systems, the sound will be localized to the speaker that provides the earliest sound.

Harmonic – A harmonic is a sound wave whose frequency is a multiple of the frequency of a reference signal. Complex sounds, such as the human voice or the sound of a musical instrument always consist of a fundamental frequency along with a number of harmonics, which, together form the basic characteristic of that sound. For example, if the fundamental frequency is 25 Hz, the frequencies of the next harmonics are: 50 Hz (2nd harmonic), 75 Hz (3rd harmonic), etc.

Harmonic Distortion – An unwanted byproduct of passing audio through an electronic device. Since it is impossible to make a perfectly linear device (where the audio out exactly matches the audio in) harmonic distortion is always a byproduct of signal processing. The less distortion a particular piece of electronics creates, the more "transparent" it is.

Head - Most often used to describe the amplifier in a two-piece amp/speaker combination. Typically, the head sits on top of a matched speaker cabinet.

Headroom - The difference between the typical level of a signal and the maximum level before the onset of clipping or other distortion. Having lots of headroom ensures that quick bursts of louder sound transients will be cleanly reproduced, increasing the overall dynamic range of the system.

Hertz (Hz) - A unit of sound frequency, named after 19th century German physicist Heinrich Hertz. If the waveform of a sound performs one complete cycle in one second's time, that sound has a frequency of 1 Hertz.

High-Pass Filter - A filter that attenuates frequencies below a certain cutoff point, while passing on frequencies above the cutoff unaffected. Sometimes called a low-cut filter.

High Fidelity – 1) A kind of sound-reproducing system whose realism of reproduction is judged to be better than average. Stereo reproduction can be high-fidelity or otherwise. 2) The pursuit of perfection in sound reproduction, as a hobby or a religion.

Hot Swap – Refers to connecting or disconnecting a device in a system while AC power is applied. Most electronic equipment is designed so that it's only safe to switch signal connections when the unit, and any attached equipment, is powered off. However, some devices are designed to be connected or disconnected while powered up. And certain connections, like USB, lend themselves to hot-swapping.

Imaging – The measure of a system's ability to float stable and specific phantom images, reproducing the original sizes and locations of the instruments across the soundstage. See "stereo imaging."

Impact - A quality of concussive force, as from a deep, strong bass attack, which produces a brief sensation of visceral pressure.

Impedance - An expression of the opposition that an electronic component, circuit or system offers to AC or DC current. Impedance contains both resistive and reactive components, although generally only the resistive part of the circuit is usually specified as Ohms. The higher the resistance, the higher the impedance.

Interface – A device that acts as an intermediary between two or more pieces of equipment. An audio interface for a computer allows signals generated by a preamplifier for example, to be communicated to the computer software.

Jitter – Jitter is the undesired deviation of some aspect of the pulses in a digital signal. Digital-analog converters (DAC) transform sample sequences (digital values) to analog voltage level sequences. In the ideal case, same time distance between the samples should be provided. The distance is defined by what we call clocking. However, clocking in not ideal and the restored signal is distorted. Jitter is thus a deviation of time between the digital and analog samples (deviation of sampling rate).

Knee–A knee is a sharp bend in an EQ frequency response or compressor gain curve.

Latency – Latency refers to unwanted time delays in audio production between when a signal enters a device or program and when it emerges. It's a common issue for digital audio workstations, where input signals must be converted to digital and then processed before reaching the monitoring stage.

Limiter – Similar in principle to a compressor, a limiter is an audio processor that prevents the amplitude of an audio signal from rising above a certain threshold, regardless of what is happening to the amplitude of the source audio. Dynamics below the threshold are more or less unaffected.

Line Level – Generally applies to the two line level references: balanced and unbalanced. Balanced or professional equipment operates at +4dBm or 1.23 volts, while unbalanced or consumer equipment operates at -10dBV or 0.32 volts. If two pieces of equipment need to be connected that use different line levels, then matching transformers should be used to equalize the levels. Otherwise the +4dBm signal will overdrive an -10dBV input and equally a -10dBV signal will not deliver enough level to a +4dBm input.

Live – 1) Describes an acoustical space having a great deal of reverberation. 2) Pertains to the sound of actual instruments or voices in performance, as opposed to the sound of their reproduction.

Load – The resistance of a device to applied power, or the device itself.

Loop – A circuit where the output is connected back to the input.

Low-Pass Filter – A filter that attenuates frequencies above a certain cutoff point, while passing on frequencies below the cutoff unaffected. Sometimes called a high-cut filter.

MIDI (Musical Instrument Digital Interface) - MIDI can be used to transmit almost every aspect of a musical performance. MIDI data is instructions about how a sound will be produced, not the actual sound itself. So, data sent from one device to another could be played with a piano sound while the original information was actually a drum sequence. MIDI has expanded beyond strictly music and can be used for lighting cues among other applications. Apart from its ubiquity, MIDI's main advantage is that file sizes are relatively small compared to what an actual audio file would be. MIDI connections are made via a five-pin DIN connector.

MP3 - Officially known as MPEG-1 Audio Layer 3, MP3 is a form of lossy data compression that can be used to create audio files that are fairly faithful to the original CD file while using only a fraction of the storage space. The MP3 codec relies on perceptual audio coding to remove audio content that our ears have trouble hearing anyway. MP3 is a popular format for streaming music services, and is compatible with most portable music players.

Microphone - A microphone is a transducer that picks up sound waves and converts them into electric current for the purpose of transmitting or recording sound.

Microphone Level – The signal level generated by a microphone, typically ranging between 0.001 to 0.005 volts. To make it usable for recording, the signal requires a microphone preamp to boost the signal up to line level.

Microphone Preamp – A circuit, stand-alone device, or section of a device designed to amplify the low-voltage signal from a microphone up to standard line level. Microphone preamps are often built into mixers and audio interfaces.

Mixer – Any device that can take two or more audio signals and mix them down to a single mono or stereo signal. Although this happens on large consoles in professional studios, home studios can achieve surprisingly professional results using digital audio workstations, which combine recording, editing, and mixing functions.

Monitor – A highly accurate loudspeaker designed for recording and mixing use. Monitors come in a variety of shapes, sizes, and configurations, and can be passive (requiring an amplifier) or active (built-in amplifiers).

Mono - Mono is short for monaural, which means only one audio channel, as opposed to stereo, which means two channels (usually a left and a right).

Near Field –Pertains to that range of listening distances in which the sounds reaching the ears are predominantly direct. See "far field," "critical distance." Generally describes a loudspeaker system that is designed to be close to the monitoring position. In this way the listener receives more of the direct sound from the speakers, while minimizing the effect of sound produced by reflections from walls, floors and ceilings.

Noise – As it applies to audio equipment, noise is unwanted sound that is not related to the signal. Noise sources can be external to a device, such as environmental noise sources. Or the noise can be generated internally. A component's signal-to-noise ratio measures how powerful the signal is in relation to the noise accompanying it.

Noise Floor – The amount of self-noise generated by a piece of electronic equipment when no signal is present. Minimizing the noise floor leads to expanded dynamic range, and cleaner recordings or sound production.

Octave – An octave is a frequency ratio of 2:1. For example, there is one octave between 100 Hz and 200 Hz, and between 1,000 Hz and 2,000 Hz. To our ears, two frequencies that are an octave apart sound like the same note. An octave band consists of all of the frequencies within an octave.

Off-Axis –Term used to describe the position of a sound source in reference to the microphone recording the source. Generally, a microphone will record best when the source is directly in front of it.

Ohm – A unit of electrical resistance.

Opaque – Lacking detail and transparency.

Open – Exhibiting qualities of delicacy, air, and fine detail. Giving an impression of having no upper-frequency limit.

Out-Of-Phase – In a two-channel system, one channel being in opposite polarity to the second, most commonly due to having one speaker hooked up with the red (positive) lead to the red (positive) terminal, the other with the red lead to the black (negative terminal). As well as a "phasey" sound, the result will be a reduction in low frequencies. See "phasey." Not to be confused with an inversion of Absolute Phase or Polarity.

Pad – A circuit designed to attenuate the output of a device by a given amount. For example, some microphones have so much output that they can overdrive the input stage of many mic preamps. To prevent this, mics often include a switchable "pad" on the output stage of the mic that reduces the mic's output by 10 or 20 dB. Some devices have built-in pads, but it is also possible to purchase external pads, which plug in to a device's output and reduce its level.

Pan – To pan means to move the perceived location of a sound source within a stereo soundstage. Generally works by reducing or making louder the particular sound source in either the left or right channel of a stereo output. If a source is panned hard left, then it will appear at only the left speaker, and likewise with the right side. The amounts of signal present in both speakers will determine the exact location of the sound source in between the left and right sides in the stereo field.

Parametric Equalizer – An equalizer whose filters contain controls over three parameters: frequency, gain/cut, and "Q," which refers to a measure of the sharpness of the resonant peak. In other words, with a narrow Q, gain or cut affects fewer frequencies adjoining the center frequency, while a wide Q will affect a greater number of adjoining frequencies.

Passive – A passive audio device doesn't have built-in power, as opposed to an active device, which does. Typical passive devices include equalizers, crossovers, and speakers.

Peak – The maximum instantaneous level of a signal. When a signal peaks beyond what a circuit can handle, distortion results.

Phantom Power – DC voltage, usually 48V that is supplied to devices with active electronics using a standard balanced microphone cable. Common devices requiring phantom power include condense microphones and direct boxes. Since the power is carried on the same wires that carry the audio signal, and since most dynamic microphones and other passive devices are not affected by this DC voltage, it became known as "phantom" power. Most mixer consoles and preamplifiers provide phantom power.

Phase – Sound is made up of waves, and when you're dealing with more than a single sound source - say, recording a source using two channels - the sound waves have to stay in sync or some of the sonic energy will be canceled. This is known as phase cancellation. A complete waveform is 360 degrees. If you have two identical waveforms and one is 180 degrees out of phase, the result will be total cancellation - silence. When capturing audio with multiple microphones, even a small delay on one mic can put the summed audio out of phase.

Pink Noise – Random noise with equal energy in all octaves. Our ears perceive pink noise as sounding relatively "flat." Because of that, and because real time analyzers tend to look at octave or 1/3-octave ranges, pink noise is a very useful audio source for measuring the frequency response of audio equipment, as well as for checking room response for sound reinforcement applications.

Polarity – Polarity is often mistakenly used interchangeably with phase, but they're two different concepts. Phase implies a relationship with time, polarity does not. So, two signals with reversed polarity are not the same as two signals being 180 degrees out of phase, although the results can be similar. What most engineers, consoles and preamps refer to as a "phase" switch is actually a switch reversing polarity.

Potentiometer – An electronic component used to provide variable control over an electronic circuit. Potentiometers are often used as volume controls on audio equipment - picture the typical rotary knob volume control. A potentiometer is often called a "pot" for short.

Preamplifier – An electronic device used to amplify low-level signals, like those from microphones, before they are fed to subsequent gain stages or devices.

Proximity Effect – Refers to the effect caused by a sound source being very close to a directional microphone. The net result is that low frequencies are boosted as the source comes closer.

Reaction – A counterforce imparted to a speaker enclosure in response to the air resistance to the motion of a moving diaphragm or cone. On a thick carpet, a reacting enclosure will rock slightly back and forth, impairing LF quality and overall detail.

Resonance - The tendency for an object or system to vibrate at a specific frequency or frequencies when excited, with the resonant frequency being determined by the physical parameters of the object or system. For example, when music is played at high volume in a space, certain features of the room may resonate to a greater extent than other aspects of the room.

Return - As it relates to audio signal processing, a return is the opposite of a send. Together, a send and return provide a path that a signal can take to be externally processed then fed back into the device. This type of send/return combination is often called an insert point.

Reverb - The sonic effect a room adds to direct sound - echoes, reflections, diffusions, and absorptions due to the room's size, shape, material, and furnishings - is called reverberation. A reverb unit (or plug-in) electronically mimics those effects, creating a sense of space, and often giving the sound a pleasing timbre and depth.

Reverberation – A diminishing series of echoes spaced sufficiently closely in time that they merge into a smooth decay.

Rumble – An extraneous low-frequency noise, often of indeterminate pitch, caused by physical vibration of a turntable or of the room in which a recording was made.

Sample or Sampling Rate –When an analog-to-digital converter captures the instantaneous amplitude of a sound source, it creates a sample. When a series of amplitude values are captured at periodic intervals, the rate is known as a "sampling rate." For example, the standard sampling rate for CD audio is 44.1kHz or 44,100 samples per second.

Send – An output on an audio device used for routing signal to an external device, such as a reverb, delay, or other processor. Typically, sends are paired with returns, which accept the signal coming back from the output of the processor.

Sensitivity – Refers to the amount of signal needed at an input for a device to deliver its rated output. A higher sensitivity means the input signal is smaller for the given output and although this is generally preferred, too much sensitivity can result in a processor being overdriven by a preceding device.

Sequencer – A device that triggers a series of events in a particular order. Today's software sequencers are typically MIDI-based.

Shelving – A type of equalizer circuit used to cut and boost a signal above or below a specified frequency, as opposed to boosting or cutting on both sides of a frequency, which is the way typical EQs operate.

Snake – A type of cabling where multiple lines are enclosed in a larger single shield. The most common use for a snake is for live sound, where microphone leads and monitor mixes are sent back and forth between the front of house mixer and the stage. Snakes are also used in recording studios.

Soundstaging - The accuracy with which a reproducing system conveys audible information about the size, shape, and acoustical characteristics of the original recording space and the placement of the performers within it.

Soundstage Shift– The apparent lateral movement of the soundstage when listening from either side of the sweet spot.

Spacious –Presenting a broad panorama of ambience, which may be wider than the distance between the loudspeakers.

Stereo Imaging – The production of stable, specific phantom images of correct localization and width. See "soundstaging," "vagueness," "wander."

Stereophonic – A two-channel recording or reproduction system.

Stereo Spread – The apparent width of the soundstage and the placement of phantom images within it. Generally, a group of instruments or voices should uniformly occupy the space between the loudspeakers. Compare "beyond-the-speakers imaging," "bunching," "hole-in-the-middle."

THD (Total Harmonic Distortion) - All electronic audio devices add some form of distortion to a signal passing through them. One form of distortion is the addition of harmonics not present in the original signal. THD measures the sum of all the harmonics added and expresses it as a percentage of the signal being measured. The closer THD is to zero, the cleaner and more transparent a device should sound.

Timbre – Pronounced “tamber,” it is the characteristic quality of sound produced by a particular instrument or voice. An oboe has a different timbre than a violin, which is why they sound different when playing the same note. Timbre is made up of all of the qualities of a sound: frequency, harmonic content, transient attack, and more. The recognizable characteristic sound "signature" of a musical instrument, by which it is possible to tell an oboe, for example, from a flute when both are sounding the same note.

Tonality – In music, the quality of an instrument's tone, often related to the key in which the music is written. In audio, mistakenly used in place of "tonal quality."

Tonal Quality – The accuracy (correctness) with which reproduced sound replicates the timbres of the original instruments. Compare "tonality."

Tracking – The degree to which a component responds to the dictates of the audio signal, without lag or overshoot.

Transducer – A device that converts energy from one form to another. Some examples of audio transducers: A microphone converts acoustic sound into electric current; by contrast, a loudspeaker converts electric current back into acoustic sound.

Transient – A very short-duration signal. Due to their speed, transients are difficult to record and reproduce accurately.

Transmission Loss – The power that is lost in transmitting a signal from one point to another. Transmission loss occurs in both wired and wireless systems.

Transparency – 1) A quality of sound reproduction that gives the impression of listening through the system to the original sounds, rather than to a pair of loudspeakers. 2) Freedom from veiling, texturing, or any other quality that tends to obscure the signal. A quality of crystalline clarity.

Ultrasonic – Beyond the upper-frequency limit of human hearing.

Uncolored– Free from audible colorations.

Unbalanced Signal – To pass an electrical signal through a wire requires two conductors. In unbalanced circuits, one conductor carries both signal and supplies ground, unlike in balanced connections, which have a third wire dedicated to ground. For this reason, unbalanced circuits are less expensive to produce, but the down side is the cables are susceptible to noise, especially with longer cable lengths.

Unity Gain – A device or setting that does not amplify or attenuate the signal is said to be at “unity gain.” Many processors are set up for unity gain; that is, they can be plugged into a system without changing its overall levels. In practice, unity gain is often a desired setting for maintaining gain staging, and for minimizing distortion and feedback.

USB (Universal Serial Bus) – A standard for interconnecting computers and peripherals. USB is a plug-and-play interface found on both Windows® and Apple® computers. It allows new devices to be configured automatically upon attachment without the need to reboot, run setups, or add adapter cards.

Voltage – Voltage is an electric charge, or potential, between two points, one being of higher relative voltage than the other is. The unit of measurement is called the “volt.” If you think of electricity as a flow of water, voltage can be thought of as the pressure, while current (amperage) would be the water volume.

WAV – Short for Waveform Audio File Formet, WAV is the standard for storing an audio bitstream on Windows-based PCs. Although a WAV file can hold compressed audio, the most common WAV format contains uncompressed audio in PCM format.

Watt – A metric unit of power defined as one Joule per second. The watt has become a common term in audio used to describe the power handling capabilities and/or requirements of speakers, and the power delivery capabilities of amplifiers.

White Noise –A sound that contains every frequency within the range of human hearing in equal amounts.

XLR – The name for a type of audio connector used for sending balanced signals and microphone feeds. An XLR connector consists of three pins housed in a barrel and often having locking components. The male side is for sends, and the female is always a receiving connector.