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Question on timbre (Sound waves)

  1. Dec 29, 2008 #1
    1. The problem statement, all variables and given/known data
    Explain why different instruments produce sounds of different quality.

    2. Relevant equations

    3. The attempt at a solution
    Different instruments produce sounds of different quality as they produce sound waves with different waveforms.


    Hi everyone! I'm new here, so I hope I have posted this in the correct section... Forgive me if its not!

    Back on topic, is my answer good enough? Do I need to mention why different waveforms produce sounds of different quality? Why does this happen anyway? How are waveforms related to timbre?

    Thanks in advance and have a Happy New Year!

  2. jcsd
  3. Dec 29, 2008 #2


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    You can start with the theory of harmonics. The ancient Greeks studied the harmonics of a vibrating string extensively. You can then consider the harmonics of an open-ended and closed-ended vibrating air column (flutes and pipe organs and such).

    What you're looking for in each of these cases is the boundary conditions on the standing waves in the various musical instruments. You get either even or odd or sometimes both even and odd multiples of the fundamental frequency.

    Various timbres occur based on were along the string or air column the instrument is struck or strummed or blown this variable will affect how strong (loud) the harmonics occur relative to the loudness of the fundamental note. Also various instruments use resonant chambers or in the cases of wind instruments, different air-column shapes which will reinforce different harmonics. Consider the shapes of the tuba vs. the saxophone vs the flute; or the shapes of the mandolin vs. the guitar vs. the bass violin.

    You then go from there to disharmonic components e.g. noise and dissonant components. For example different bell shapes will have different resonances which may not fall on the series of harmonics overtones of the fundamental note. The extreme cases are the clashing sound of gongs and cymbals.

    Along with these components is the introduction of "white" and "pink" noise (randomized frequency components) The blowing of your breath on a wind instrument and the "roughness" of reeds in say a saxophone or clarinet gives you the whispering sound technically called noise. The extreme example is what you get when you tune an analogue TV to a blank channel (white noise).

    Finally electronic instruments allow you to control their timbres electronically and introduce various noise and distortion effects.
  4. Dec 29, 2008 #3
    Thanks for your reply, James!

    So is it correct to infer that the timbre is directly affected by the shape of the instruments? So different shapes produce different waveforms, but the exception is pink noise?
  5. Dec 29, 2008 #4
    In the case of electronic instruments, the shape doesn't matter much. ;)

    What James said was correct, but I'll put it another way, if it helps.

    Timbre is the collection of frequencies in a sound. We think of a musical note as being one specific pitch, or frequency. But a musical instrument playing one note actually produces many, many different frequencies. It is the unique balance of frequencies that makes up the distinctive timbre of a particular instrument (or a particular way of playing it).

    There are many things that can influence the timbre. The shape of the instrument is one of them, since it will accentuate some frequencies and attenuate others. The method of "attack" is another. Consider the difference in timbre between a harpsichord and a piano, where the major different is that the harpsichord plucks the strings, whereas the piano hits them with a hammer. Then, of course, there are the characteristics of what, exactly, is doing the vibrating (a piano string, a reed in a saxophone, a drum head, etc.).
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