SOUND ON SOUND
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A form of electrical filter which is designed to mimic the relative sensitivity of the human ear to different frequencies in terms of pereceived loudness. It is broadly similar to the A-Weighting curve, except that it adds a shelf boost above 2kHz. This filter is an integral element of the ITU-R BS.1770 loudness measurement protocol. (See also A-Weighting and C-Weighting.)
A form of electrical filter which is designed to mimic the relative sensitivity of the human ear to different frequencies at high sound pressure levels (notionally 100 Phons or about 87dBA SPL). Essentially, the filter rolls-off the low frequencies below about 20Hz and the highs above about 10kHz. This filtering is often used when making measurements of high-level sounds, such as when calibrating loudspeaker reference levels. (See also A-Weighting and K-Weighting.)
When the length of an electrical cable is shorter than about 10% of the wavelength of the signal it conveys, the voltage and current are effectively the same at all points along the cable. However, if the cable is longer than 10% of the wavelength, the signal can be considered to propogate as electromagnetic waves along the cable, and this condition is referred to as a 'transmission-line'.
An additional dedicated mixer input channel, usually with minimal facilities, designed to accommodate the output from an external effects unit. (cf. Aux Return)
A subjective term used to describe sound, where the bass and low-mid frequencies have depth and where the high frequencies are smooth-sounding rather than being aggressive or fatiguing. Warm-sounding tube (valve) equipment may also exhibit some of the aspects of compression.
An form of equaliser whereby multiple narrow segments or bands of the audio spectrum are controlled by individual cut/boost faders. The name comes about because the fader positions provide a graphic representation of the EQ curve. The bandwidths of the filters are typically octave (10 faders) or 1/3 octave (31 faders).
The physical construction which encloses and supports the loudspeaker drive units. Usually built of wood or wood-composites (although other materials are often used including metal alloys and mineral composites). Cabinets can be ‘sealed’ (often referred to, misleadingly, as an 'infinite baffle') or ‘vented’ in various ways (ported, bass-reflex, ATL, transmission line), the precise design influencing the bass and time-domain characteristics.
Any box-like construction will resonate at one or more frequencies. In the case of a loudspeaker, such resonances are likely to be undesirable as they may obscure or interfere with the wanted sound from the drive units. As resonance also involves the storing and releaseing of energy over time, cabinet resonances can result in 'time smearing', causing a sharp impulsive sound like a 'thud' to be reproduced as a prolonged 'boom'. Cabinets are usually braced and damped internally to minimise resonances.
A passive, two-terminal electrical component which stores energy in the form of an electrostatic field. The terminals are attached to conductive ‘plates’ which are separated by a non-conductive dielectric. Capacitance is measured in Farads and the amount of capacitance depends upon the size of the plates and the spacing between them. If a voltage is applied across the terminals of a capacitor a static electric field develops across the dielectric, with positive charge collecting on one plate and negative charge on the other. Where the applied voltage is an alternating signal, a capacitor can be thought of as a form of AC resistance that reduces with increasing signal frequency. The old-fashioned term is a ‘condensor’.
Also known as a 'condenser microphone'. This is a specific form of electrostatic microphone which operates on the principle of measuring the change in electrical voltage across a capacitor which contains a constant static charge. The capacitor is formed from two metal electrodes, one fixed (the back-plate) and the other a thin conductive membrane that flexes in response to sound pressure, and the static charge comes either from a DC-bias voltage or a dielectric material. (See also 'Back Electret', and 'RF Capacitor Microphone'.)
An open-celled expanded polyurethane or melamine foam that allows sound waves to enter and flow through the foam to dissipate their energy and thus prevent the sound waves from being reflected. The density and depth of the foam affects the frequency range over which it is effective as an acoustic absorber.
A general term embracing a range of products or constructions intended to absorb, diffuse or reflect sound waves in a controlled manner, with the intention of bestowing a room with acceptable reverberation times at all frequencies, and a neutral overall sound character.
The term typically describes an electronic circuit containing transistors, integrated circuits (ICs), tubes or other devices that require power to operate, and which are capable of amplification. Also used to describe loudspeaker monitoring systems which employ separate amplifiers to power each drive unit individually.
A device which converts an analogue audio signal into a digital representation. (Cf. D-A Converter.) (An explanatory video is available when subject link is clicked.)
A widely used eight-channel optical digital audio interface developed by Alesis as a bespoke interface for the company's digital eight-track tape machines in the early 1990s (Alesis Digital Audio Tape). The interface transfers up to eight channels of 24-bit digital audio at base sample rates (44.1 or 48 kHz) via a single fibre-optic cable. This 'lightpipe' and its conenctors are physically identical to that used for the TOSlink optical S/PDIF stereo interface found on many digital consumer hi-fi devices. However, while the light-fibre itself can be used interchangeably for either format, the S/PDIF and ADAT interfaces are not compatible in any other way.