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My homemade guitar was producing perfect sine waves, most guitar waves arent perfectly sine. Anyone have any suggestions for why? Physics project))

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    That's surprising. How do you know that it was producing perfect sine waves?
    – badjohn
    Jun 3, 2017 at 23:04
  • To me, that would be a sign that my strings were shot and needed to be replaced.
    – NReilingh
    Jun 4, 2017 at 1:45
  • Perfect? What did you use to measure the harmonic distortion?
    – Simon B
    Jun 4, 2017 at 22:19
  • Related question.
    – guidot
    Jun 6, 2017 at 12:18

1 Answer 1

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All string and wind instruments produce pure sine waves. The thing is, usually they produce more than one of them at a time, at multiples of the root. For example, if a string 12" long produces a sine wave, it will also produce the same sine wave that would be produced at 6", and at 4". These are called harmonics. When you combine these, the waves don't look like sine waves any more-- if you combine enough harmonics in the right proportions, you could eventually get a square wave, for example.

Harmonics can be removed by using a low pass filter. If you adjust the filter to remove all the harmonics, you will always be left with a single sine wave at the note's root.

My guess is that you recorded your guitar under some form of EQ, filter, or other signal processing effect, and only the fundamental made it through to the stage where you were examining the waveform.

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  • For a plucked string fixed at both ends at least, these harmonics are a given, as the waves reflect and interfere. Also, the location of the pluck will impact the harmonics. So I tend to agree: the "perfect sine wave" is either imaginary or the result of filtering.
    – Yorik
    Jun 6, 2017 at 14:41

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