- published: 01 Apr 2016
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Noise in audio, recording, and broadcast systems refers to the residual low level sound (usually hiss and hum) that is heard in quiet periods of a programme.
In audio engineering it can refer either to the acoustic noise from loudspeakers, or to the unwanted residual electronic noise signal that gives rise to acoustic noise heard as 'hiss'. This signal noise is commonly measured using A-weighting or ITU-R 468 weighting
Noise is often generated deliberately and used as a test signal. Two types of deliberately generated noise in common use are referred to as 'white noise', which has a uniform spectral power density at all frequencies, or 'pink noise' which has a power spectral density that falls at 3dB/octave with rising frequency. The latter is often more useful in audio testing because it contains constant energy per octave (and hence per commonly used 1/3rd octave), rather than a prepondance of energy at high frequencies. In other words it contains energy that is distributed geometrically rather than linearly.
In common use, the word noise means any unwanted sound.
In physics and analog electronics, noise is a mostly unwanted random addition to a signal; it is called noise as a generalisation of the acoustic noise ("static") heard when listening to a weak radio transmission with significant electrical noise. Signal noise is heard as acoustic noise if the signal is converted into sound (e.g., played through a loudspeaker); it manifests as "snow" on a television or video image. High noise levels can block, distort, change or interfere with the meaning of a message in human, animal and electronic communication.
In signal processing or computing it can be considered random unwanted data without meaning; that is, data that is not being used to transmit a signal, but is simply produced as an unwanted by-product of other activities. "Signal-to-noise ratio" is sometimes used to refer to the ratio of useful to irrelevant information in an exchange.
In biology, many different forms of cellular noise exist, where a measurement displays substantial variance around its mean: for example, transcriptional noise describes the variability in gene activity between cells in a population.
Audio is an electrical or other representation of sound.
Audio may also refer to: