Old terms to new, we’ve compiled a big ‘ole list of audio and audio engineering terms. Search away:
Absorption The loss of energy from a sound wave caused by friction with the air or porous material.
AC Alternating current. An electrical current that reverses direction in a periodic manner.
Acoustic Treatment The application of absorbent material to the surface of an enclosure to modify the acoustics.
Acoustics The science of sound. The property of an enclosure in relation to sound.
ADC Analog-to-digital conversion.
Aliasing See Nyquist limit.
Ambient Sound The noise, reverberation or atmospheric sounds that form a background to a sound source.
Amplifier A device by which the strongth of a signal can be modified.
Amplitude The peak value of a waveform.
Analog A signal which resembles the original waveform that created it.
Anechoic With reverberation. An anechoic chamber is an enclosure in which there are no audio-wave reflections.
Attack time The time taken for the gain reduction to take effect in a compressor or limiter.
Audio Within the normal range of human hearing, about 20 to 20000 kHz.
Azimuth The angle between a head gap and the longitudinal axis of the analog tape.
Balance The achievement of the correct relationship between the various components of a sound source and the acoustic environment to produce the required artistic effect.
Bass. The lower frequencies in the audio spectrum.
Beats The periodic variations of amplitude resulting from the combining of two periodic waveforms of similar kind but slightly different frequency.
Bel A scale used to describe the relative magnitude of powers. It is equal to the logarithm to the base 10 of the ratio of the powers. It is used extensively in audio work to describe the level of a signal in relation to a set datum. For audio purposes the bel is too large a unit and the decibel (one tenth of a bel) is used. One dB represents just about the smallest change in audio level discernible to the human ear.
Bias In magnetic recording, the superimposition of a steady magnetic field on the program signal magnetic field to bring the signal excursions to a straight part of the magnetization transfer characteristic, thereby avoiding non-linear distortion and increasing the output.
Bias compensation In phonograph tone arms, a small torque is applied, usually by a spring or a small weight on a string, to compensate for the tendency for the arm to be drawn towards the centre of the record bv the drag of the pick-up in the groove.
Bi-directional A microphone with a figure-of-eight directivity pattern.
Binaural hearing The ability to perceive the direction of a sound source, either directly or by electroacoustic means whereby the two ears are supplied with separate transmission channels. Microphones for binaural sound are usually embodied in a dummy head, or separated by a small baffle to simulate the natural condition.
Bit Contraction of ‘binary digit’, the basic digital unit. Eight bits make a ‘byte’.
‘Bitstream’ conversion Instead of measuring the signal 44100 times a second (which would provide for 65536 [2 101 possible values of analogue level, converts the 16-bit digital signal into a high-speed ‘-bit data stream, extracting the most significant bit and measuring the change of level, up or down, effectively doing 256 calculations each second on each of the 44100 digital words available, creating a single bitstream with a frequency of 11.3 MHz, equivalent to 256 times oversampling. The intention is mainly to improve the low-level response where errors in significant bits could cause serious distortion. However, the process causes its own degree of noise and distortion but this is spread over the whole 11.3 MHz spectrum and can be shifted from the audio spectrum by ‘noise shaping’, using the 15 ‘discarded’ bits.
Capacitor A component made up of two conducting plates separated by
insulation. Capacitors present a decreasing impedance to alternating current as the frequency is increased.
Capacitor microphone Also called condenser or electrostatic microphone. A microphone in which the pressure of sound waves varies the capacitance between the diaphragm and a fixed back plate. It is fed with a polarizing voltage in series with a high resistance across which the output is generated.
Capstan Drive spindle of a tape machine. Traction is achieved by the pinch wheel pressing the tape against the capstan.
Cardioid microphone A microphone with a heart-shaped directivity pattern.
Chromium dioxide A type of magnetic tape coating which permits the recording of higher levels of high frequency than regular (ferric oxide) tape, but requ ires a different value of bias.
Coincidant pair An arrangement of microphones for stereophony, in which two microphones are placed with their diaphragms close together, possibly in the same housing, but facing different ways.
Companding The application of compression to a signal before a process le.g. recording); and expansion afterwards to reduce the system noise of the process.
Compressor A variable-gain amplifier, in which the gain, above a set threshold, is controlled by the input signal. It is used for reducing the dynamic range of the signal.
Crossover frequency The frequency at which equal power is delivered to both outputs of a dividing network. In the case of loudspeakers the same power would be applied at this frequency to both the ‘woofer’ (low frequency loudspeaker) and the ‘tweeter’ thigh-frequency unit). Above and below this frequency the two units begin to take over, one from the other.
Crystal (piezo-electric) A crystalline substance (usually of rochelle salts, quartz or tourmaline) which has the property of generating small voltages when physically stressed. Used in some microphones and phonograph pick-up heads.
Cycle One complete sequence of a variation which occurs in a periodic manner. One cycle per second is one hertz (Hz).
DAC Digital-to-analog converter.
DASH recorder Digital audio recorder with stationary head. A very highquality recording system, often used for mastering phonograph records.
dBA A scale, used for measuring noise, that takes into account the unequal sensitivity of our hearing to the audio frequency spectrum.
DBX A noise reduction system which employs pre-emphasized compression before recording and de-emphasized expansion afterwards.
Decibel See bel.
De-emphasis A response that decreases as frequency increases. (The opposite of pre-emphasis.)
Digital sound A process for dealing with audio in which the original analog waveform is converted into a series of numerical measurements which can be described by a digital code, usually binary, for which the processing equipment only has to recognize two states: 1 (on) or 0 (off).
Dolby A noise reduction process named after its inventor, Dr Ray Dolby.The Dolby A system is a frequency-selective companding arrangement, used before and after professional recording equipment especially for the production of master tapes. Dolby Band C are processes applied to commercial records on the assumption that complementary equipment will be used for replay. Dolby SA (Spectral Recording) is similar to Dolby C except that three levels of action staggering are used: high, mid and low level. The main principle is to apply the companding action only at the frequencies where it is needed at each instant and to keep the low-level components of the signal boosted at all times.
Dubbing The process of re-recording from one recording to another. Sometimes used for the addition of sound (e.g. foreign dialogue) to a previously recorded picture.
Dynamic range The ratio between the softest and loudest sound. Or the ratio of the signal variation available between unacceptable noise level and overload. (Expressed in decibels.)
Echo Discrete, separately ident ifiable repetitions of sound due to reflection of sound waves from hard surfaces. The term is often used. wrongly, to mean reverberation. which is due to multiple overlapping reflections. which blend together to prolong the sound.
EFM Eight-to-fourteen modulation, a technique which converts each 8-bit into a 14-bit symbol, with the purpose of aiding the recording and playback procedure by reducing the required bandwidth, reducing the signal’s DC content and adding extra synchronizing information. The procedure is to use 14-bit codewords to represent all possible combinations of the 8-bit code. An 8-bit code represents 256 (i.e. 2a) possible combinations. A 14-bit code represents 16384 (2 a ) different combinations. Out of the 16384 14-bit codewords only 256 are selected, having combinations which aid processing of the signal. For instance, by choosing codewords which give low numbers of individual bit conversions (i.e. 1 to 0 or 0 to 1) between consecutive bits the bandwidth is reduced. Also by choosing codewords with only limited numbers of consecutive bits with the same logic level the overall DC level is reduced.
Eigentone. Standing-wave resonances in an enclosure when the reflective path length coincides with the wavelength of a sound.
Equalization (EQ) The process of modifying the amplitude/frequency response to correct for amplitude distortion or to minimize noise. The term is also used for the deliberate distortion, or shaping, of a sound signal for artistic effect.
Flutter A periodic pitch variation with a repetition rate greater than 10 times per second. A slower repetition is called ‘wow’.
Frequencv The rate of repetition of a periodic fu nction, measured in hertz (Hz).
Frequency modulation A method of modulating a carrier by varying its frequency as opposed to its amplitude.
Gain Amplification of a component. Usually expressed in decibels.
Haas effectThe effect that determines the apparent di rect ion of a source of sound. When the same sound is reproduced simultaneously from two or more places it w ill appear to come entirely from the nearest one, unless another source is very much louder. The relationship between sound volume. time delay and directionality is known as ‘Haas effect’.
Harmonic A sinusoidal oscillation having a frequency which is an integral multiple of the fundamental frequency. It is the harmonics (or in musical terms upper partials) that shape the waveforms and make it possible to distinguish between various instruments, even when they are playing the same note.
Harmonic distortion The production of spurious harmonics due to irregularity in signal processing distorting the original waveform.
Hertz (Hz) Unit of frequency. One hertz equals one cycle of repetition per second.
Hypercerdioid Directional response (polar diagram) between cardioid and figure-of-eight. For example a microphone with hypercardioid response would have a narrower than cardioid acceptance angle in front, with a small lobe at the back.
Impedance The restriction of current due to the total resistance and reactance of a circuit.
Intermodulation distortion A form of distortion caused by the mixing of component frequencies, in which one frequency modulates another, causing the production of spurious tones and a general roughness of the sound.
Limiter A device for preventing the volume of a signal from rising above a pre-set value, to allow a higher average level to be accommodated without overload.
Loudness The subjective auditory impression of the intensity of a sound.
MADI Multi-channel audio digital interface. Carries a number of channels of audio over a single coaxial cable or optical fibre.
Masking The process by which the ability to hear sound of a particular frequency is reduced by the presence of louder sounds of similar frequency.
MIDI Musical instrument digital interface. A standard interface protocol, used to link instruments and computer systems, e.g. electronic keyboards, drum machines, and audio processing devices.
Modulation The control of one waveform by another.
Monaural, monophonic, or mono A single-channel sound system.
Moving coil A transducer system based upon the movement of a coil of wire in a magnetic field.
Nyquist limit In converting an audio signal between analog and digital format the sampling frequency must be at least twice the highest frequency it is intended to convert. This is the Nyquist limit. If it is not exceeded a form of heterodyning, called aliasing, will occur, caused by beating between the input and the sampling frequency. In practice the sampling rate has to be at least 2.2 times the highest audio frequency to allow for filtering out the out-of-band components of the audio signal.
Ohm Unit of resistance or impedance.
Ohm’s Law General law describing the flow of direct current in an electrical circuit. It states that the magnitude of the current (in amperes) is proportional to the potential difference (in volts) divided by the resistance (in ohms).
Omnidirectional Acting equally in all directions.
Oversampling When converting between digital and analog it is necessary to use a sampling rate at least twice the highest frequency it is intended to convert (see Nyquist Limit). Oversampiing is a method of increasing the effective sampling rate by interpolation.
Pan pot Panoramic potentiometer. A control used in stereophony for adjusting the apparent lateral direction of a sound source.
Parametric equalizer A frequency·shaping device, which can boost or reduce a signal at a particular frequency. The position on the scale and the width of the peak or trough in the response can be varied.
Phase The position in the cycle that a waveform has reached at any given instant. Waves are said to be in phase when their position in the cycle coincides.
Phon A measure of the loudness of a sound that takes into account the unequal sensitivity of our ears to sounds of different frequencies. The decibel scale of aural sensitivity (equal loudness/frequency) is the same as the phon scale at 1000 Hz, but differs at other frequencies.
Pitch Subjective auditory sensation of sound related to a scale mainly of frequency, but also influenced by such factors as intensity and harmonic structure.
Pre–emphasis Boosting the high-frequency component of a signal before recording, or (FM) transmission, so as to reduce the high· frequency system noise when it is subsequently de-emphasized on reproduction.
Pulse code modulation (PCM) A system for converting the audio signal into a series of pulses. The analogue waveform is sampled at a fixed rate, the amplitude of each sample being represented by a binary word of fixed length (typically 16 bits).
Reverberation The sustaining effect of multiple sound wave reflections within an enclosed area, with reflecting surfaces. It is quantified in the time in seconds that a sound takes to die away to one millionth (-60dS) of its original power after it has been cut off abruptly.
Sine wave The pattern executed by a simple cyclic variation, such as an alternating current. In audio terms it is a pure tone.
Stereophony A two·channel audio system which can provide the impression of spatial distribution of sound sources in the horizontal plane.
Time constant A method of stipulating the shape of a frequency correction curve by the charge/discharge time, quoted in microseconds, of a circuit containing resistance and capacitance.
Tone arm (tracking arm) The arm that supports the pick-up in a phonograph.
Transducer A device for converting one form of energy into another, e.g. alternating electrical signals into mechanism movement, or vice versa.
Tweeter The high-frequency element in a multi-unit loudspeaker system.
VCA Voltage controlled amplifier. The gain of a VCA is controlled by a small DC voltage applied by a fader in a sound control console, thereby reducing the risk of noise caused by poor contact when programme is routed through faders.
VU meter A meter for indicating programme volume.
Waveform The shape of a graph depicting the successive values of a varying quantity.
Wavelength The distance between corresponding parts of a waveform.
White noise A full-spectrum signal having the same energy level over the whole audio frequency range.
Woofer The low-frequency element in a multi-unit loudspeaker system.
Wow A slow variation of pitch, normally most noticeable on sustained low notes, usually due to eccentricity in tape recorder or turntable drive system or enlarged centre holes in discs.