Noise (audio)
Encyclopedia
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 audio engineering
Audio engineering
An audio engineer, also called audio technician, audio technologist or sound technician, is a specialist in a skilled trade that deals with the use of machinery and equipment for the recording, mixing and reproduction of sounds. The field draws on many artistic and vocational areas, including...
, 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
A-weighting
A Weighting curve is a graph of a set of factors, that are used to 'weight' measured values of a variable according to their importance in relation to some outcome. The most commonly known example is frequency weighting in sound level measurement where a specific set of weighting curves known as A,...
or ITU-R 468 weighting
ITU-R 468 noise weighting
ITU-R 468 is a standard relating to noise measurement, widely used when measuring noise in audio systems. The standard defines a weighting filter curve, together with a quasi-peak rectifier having special characteristics as defined by specified tone-burst tests...
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
White noise
White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
', which has a uniform spectral power density at all frequencies, or 'pink noise
Pink noise
Pink noise or 1/ƒ noise is a signal or process with a frequency spectrum such that the power spectral density is inversely proportional to the frequency. In pink noise, each octave carries an equal amount of noise power...
' which has a power spectral density
Spectral density
In statistical signal processing and physics, the spectral density, power spectral density , or energy spectral density , is a positive real function of a frequency variable associated with a stationary stochastic process, or a deterministic function of time, which has dimensions of power per hertz...
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.