Whats noise?

[sq225917]

What's the definition of noise in audio? Is it the random nature, the distribution vs frequency and amplitude, a lack of correlation to the signal?

 

[dc655321]

What's the definition of noise in audio?

Katy Perry et al

 

[jae]

Noise (electronics) - Wikipedia

en.wikipedia.org

 

[dc655321]

What's the definition of noise in audio? Is it the random nature, the distribution vs frequency and amplitude, a lack of correlation to the signal?

You've listed some characteristics of noise, but are you talking about electrical or acoustic noise? Or both?

I would define noise as output in the absence of input. This gives the lack correlation with input from your list.
Noise can be characterized by its power spectrum.

Look up the relationships between power law and Gaussian functions with their Fourier transforms (eg here).
Fascinating stuff.

 

[iMickey503]

The sound that your tape deck makes when its not playing any music. Sounds like "Hisssssshshshshshssh

 

[syn08]

In general, noise is an error which is superimposed on top of a useful signal. Noise may be random (aka correlated or partially correlated) or systematic. Usually, noise is classified by type (additive, multiplicative, white, black, red, brownian, Gaussian, Cauchy, etc… each with its own mathematical description) and by the source origin (Johnson, cosmic, 1/f, quantum, Barkhausen, EM, etc… etc... etc… each being of a certain type).

Audio noise is any unwanted perturbation that comes on top of the useful signal. These perturbations can be of any type and any source, the only specific property is their limited bandwidth, to audio frequencies, so many high frequency noise sources can be safely ignored.

Sorry, your question is too fuzzy to further expand. Short answers, audio noise is not necessary random, the distribution of frequency and amplitude is not necessary relevant, and correlation (or not) with the signal is not specific to audio noise. Example, hum is a highly correlated (aka systematic) noise source of EM origin, tape hiss is a mixture of Barkhausen, 1/f, a few other sources, and is little correlated (aka random).

 

[BostonJack]

In general, noise is an error which is superimposed on top of a useful signal. Noise may be random (aka correlated or partially correlated) or systematic. Usually, noise is classified by type (additive, multiplicative, white, black, red, brownian, Gaussian, Cauchy, etc… each with its own mathematical description) and by the source origin (Johnson, cosmic, 1/f, quantum, Barkhausen, EM, etc… etc... etc… each being of a certain type).

Audio noise is any unwanted perturbation that comes on top of the useful signal. These perturbation can be of any type and any source, the only specific property is its limited bandwidth, to audio frequencies, so many high frequency noise sources can be safely ignored.

Sorry, your question is too fuzzy to further expand. Short answers, audio noise is not necessary random, the distribution of frequency and amplitude is not necessary relevant, and correlation (or not) with the signal is not specific to audio noise. Example, hum is a highly correlated (aka systematic) noise source of EM origin, tape hiss is a mixture of Barkhausen, 1/f, a few other sources, and is little correlated (aka random).

Good answer. Noise may also be intentionally introduced, in audio circuits, that would most often be 'pink' (i.e. 1/f noise) or 'white' depending upon the spectral density. Thermal noise sets a fundamental limit dependent upon the impedance and temperature of a particular circuit. Once you scratch the surface, its a complex topic. Some signal processing techniques allow extraction of signal whose power is actually lower than the noise in a particular circuit. (used more often by Three Letter Agencies than audio engineers). Plus, there is audio steganography which will inject a signal that appears to be noise, without the knowledge of how to decrypt it. Its all good fun.

 

[clearnfc]

What's the definition of noise in audio? Is it the random nature, the distribution vs frequency and amplitude, a lack of correlation to the signal?

Under perfect scenario, your speakers will be producing absolutely no sound when amp inputs are not connected (regardless of volume).

However, all electronics do produce some kind of unwanted noise, hissing being the most common. You can try disconnecting your amp imputs and turn up the volume, there will be some hissing from your speaker. Thats unwanted sound (noise).

Its unavoidable though. Nothing is perfect. Eg, transistors and capacitors have very small amount of leakage current.