An alternative form of capacitor microphone which uses the capacitive capsule as the tuning element of a radio-frequency oscillator. Sound waves arriving at the capsule change its capacitance, which varies the frequency of the RF oscillator to produce an FM signal. This is immediately demodulated by the microphone's internal circuitry to produce the audio output. The advantage of this approach is that the capsule works in a very low-impedance environment (as opposed to the very high-impedance environment of a traditional DC-biased and Electret capacitor mics), making it immune to the effects of humidity which can cause unwanted noise in conventional capacitor mics. This technology was invented by Sennheiser and is used in their MKH range of microphones.

Unwanted interference into an audio system from external RF signals.

An abbreviation for Radio Frequency.

The time taken for sound waves reflecting within a space to lose energy and become inaudible. A standard measurement is ‘RT60’ which is the time taken for the sound reflections to decay by 60dB.

Short for Reverberation. The dense collection of echoes which bounce off acoustically reflective surfaces in response to direct sound arriving from a signal source. Reverberation can also be created artificially using various analogue or, more commonly, digital techniques. Reverberation occurs a short while after the source signal because of the finite time taken for the sound to reach a reflective surface and return - the overall delay being representative of the size of the acoustic environment. The reverberation signal can be broadly defined as having two main components, a group of distinct ‘early reflections’ followed by a noise-like tail of dense reflections.

The characteristic of a filter that allows it to selectively pass a narrow range of frequencies. See Q.

Opposition to the flow of electrical current. Measured in Ohms.

The time taken for a signal level or processor gain to return to normal. Often used to describe the rate at which a synthesized sound reduces in level after a key has been released. Also used to describe the time taken for a compressor top restore unity gain after a signal has fallen below the threshold. Also known as ‘recovery time .‘

The way in which sound waves bounce off surfaces.

A term used to imply a standard audio CD. The name comes from the fact that the original specifications documents for the audio CD created by Sony and Philips had a red cover! Recordable CD-Rs are described as 'orange book' for similar reasons.