Noise (audio)

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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 program.

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.

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