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In acoustics, what is the difference between a tone and a noise? I have been trying to find a definition of these terms. So far, the best I have come up with is

  • A tone is a sound that can be described as linear combination of sine and cosine waves.
  • A noise is a sound that is not a tone.

Does this definition make sense? I am uncertain if this definition of noise is too restrictive.

See here for a comparison between tone and noise. See here for where I found the comments on linear combinations.

  • The definition of noise might vary depending on the context. The definition you are showing is maybe appropriate in the context of music, but in signal processing, the definition might be different. en.wikipedia.org/wiki/Noise_%28signal_processing%29 – audionuma Sep 6 '15 at 7:21
  • @audionuma Can you explain what the signal processing version might be? – Stan Shunpike Sep 6 '15 at 7:35
  • I couldn't explain it better than the link I provided, or alternative ones that you could find. – audionuma Sep 6 '15 at 7:38
  • Are you asking about 'Noise' or 'A noise'? Because 'A noise' is any unwanted sound really. Or a sound with an unknown source. So it could be a tone in that definition. But in signal processing, my definition is; A tone has a fundamental frequency, but noise does not. – Marc W Sep 13 '15 at 4:27
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In response to another answer, noise should definitely not be replaced with sound.

A tone generally refers to a single frequency. Sound is a general term, but would usually be used when you are talking about a single tone or collection of tones.

The distinction between sound and noise depends on your perspective: there is the signal you want and the signal you don't want. Sound would be the signal you want, and noise the signal you do not want.

Noise is often modeled as a random process, but this is not always true. When using analog electronics to monitor someone's heartbeat, the signal you want is the person's heartbeat. Noise manifests in the form of a 60 Hz sine-wave (sometimes harmonics as well), which will become present when viewing the person's heartbeat.

  • Thank you for clarifying. This makes a lot more sense than the other user's reply. – Stan Shunpike Sep 7 '15 at 5:17
  • There are cases where noise is a wanted sound: noise generators for profiling, noise used artistically in compositions and productions (the analog touch), noise used as basis for further sound synthesis (snares, cymbals etc), noise used for dithering.. probably many other examples. You could say that by definition it is not noise then (because it is wanted), but I think that contradicts common use of the term 'Noise'. – Michael Hansen Buur Sep 8 '15 at 10:42
  • I didn't say that noise is an unwanted sound; it is an unwanted signal. Most of the confusion here is just a matter of definitions, and in engineering noise is is an unwanted signal, but it is also used to talk about a broadband signal like white noise. – soultrane Sep 9 '15 at 1:35
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I think perhaps this would be better/more accurate if the term noise were swapped out with the term sound instead.

A tone is a noise (sound), generally associated with one particular frequency or note.
A noise (sound) does not necessarily consist of just one single tone.

For instance: The note, "A" is a tone which resonates @ the frequency - "440Hz".

In most technical contexts, the term noise typically arouses the connotation of uselessness or un-usefulness and is often considered garbage or interference. An quick example of this is prevalent in the expanded term "signal to noise ratio".

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