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Definition of overtones
Hello,
Could you give me a rough definition of what are overtones? Is sustain part of the equation? I am sorry if this is a dumb question, I have read the definitions on other web sites, but I am looking for the layman's explanation. Thanks in advance for your feedback.
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Mike C. |
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'Common-sewer' of unrefined guitars. |
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We usually think of a string as sounding at one 'fundamental' pitch: A=110 Hz (cycles per second), for example. Really, though, a string can vibrate at quite a large number of frequencies, all at the same time, and usually does. 'Ideal' strings, the kind that only exist in physics books, vibrate in frequencies that are exact multiples of the fundamental, so the A string would vibrate not only at 110 Hz, but 220, 330, 440, 550, and so on. When the frequencies are exact multiples like that (and _only_ then), they're called 'harmonics'.
Real strings don't do that. For one thing, real strings have some stiffness, and that shifts the frequencies of the higher vibrations upward in pitch a little from where they 'should' be. Since they're not behaving themselves and being really 'harmonious', we call those higher pitches above the fundamental 'overtones'. It's easy to hear these, of course. The fundamental has the whole length of the string moving in the same direction at any one time, and the overtones break it up into shorter sections. Touching the string at the 12th fret divides it into two equal lengths, and sounds the first overtone above the fundamental, roughly an octave higher in pitch (near 220 on the A string). Touching at the 7th fret splits the string length into thirds, and you get the second overtone above the fundamental, a 12th (octave plus a fifth higher) at around 330 Hz, and so on. Another way that you'll often see these things refered to is as 'partials': the fundamental is the 'first partial', the octave overtone is the 'second partial' and so on. Any time you play a string there will be some energy in the overtones, but how much will depend on where you play the string. If you pluck it right over the 12th fret, you're telling the string to move at a point where the octave overtone 'wants' it to be still, so there won't be much energy in that overtone. In fact, there won't be much energy in any of the 'even order partials', the ones that are even multiples of the fundamental frequency. That's why the string sounds the way it does when you pluck it there. Generally speaking, the closer to the end you pluck, the more energy there will be in higher overtones, and the less in the fundamental. That extra high frequency energy accounts for the 'bright' and 'cutting' sound when you play close to the bridge. Then there's the whole issue of what the guitar _does_ with that energy, but we'll leave that for another post... |
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A Goodall.
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The Big Fat Lady 02' Gibson J-150 The Squares 11' Hummingbird TV, 08' Dove The Slopeys 11' Gibson SJ (Aaron Lewis) The Pickers 43' Gibson LG-2, 09' Furch OM 32SM (custom) , 02' Martin J-40 The Beater 99' Cort Earth 100 What we do on weekends: http://www.reverbnation.com/doubleshotprague |
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- Glenn |
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- Glenn |
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Thanks for the quick responses.
I guess my next question is, are they desirable or not? My main reason for posting the original question is that when I play my new 814ce with other people plugged in and I strum hard, I can hear the low strings quite loud the sound is almost pleasant, but if I go overboard it starts becoming unpleasant. Last night I was strumming the guitar hard unplugged at home and at one point in time it started sounding unpleasant and I am wondering if that is what some people call the overtones of rosewood. By the way I love the guitar and that one is staying with me for life, I love the way it sounds, the above is more of a quest for learning to play the instrument the right way, it is in no way a criticism of the guitar. Thanks.
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Mike C. |
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Alan, please check my understanding of terminology here.
If I touch the string at the 12th fret and pluck it, isn't the resulting sound the second (even) harmonic? IOW isn't what you call the "first overtone" the second harmonic? Is the definition of "overtone" different than that of "harmonic"? One other nit to pick: When the fundamental is suppressed, as described, isn't the resulting sound actually the sum of the second harmonic and all of the higher, even numbered harmonics, not just the second harmonic?
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Yours truly, Dave Morefield A veteran is someone who at one point in his or her life wrote a blank check made payable to 'The United States of America' for an amount of 'up to and including my life.' |
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"Use what talents you possess; the woods would be very silent if no birds sang except those that sang best." Henry Van Dyke "It is in the world of slow time that truth and art are found as one" Norman Maclean, |
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they can be very desirable or not, depending on individual preference and the use that particular guitar will have. for example, overtones aren't always so good if you'll be playing leads, but can add a really beautiful sound for some fingerpicking.
btw, i've never found that overtones are unpleasant at any time. sounds like maybe you overdrove (is that even a word?) your guitar. Quote:
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Although this is a sweeping generalization that shouldn't be taken too literally, top woods like cedar or redwood have less headroom than spruces. Among the types of spruce, Engelmann will often have less headroom while red (Adirondack) spruce has more. Again, it depends on each individual piece of wood but that's the general tendency on average. Redwood, cedar and Engelmann are still great woods and they can respond especially well to light input. But headroom isn't their primary strength and they may distort if played too hard (again, not always; just talking about the average tendencies of woods here). Sitka and European spruces often seem to be balanced, responding fairly well to light input and having fairly high headroom.
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Bob DeVellis |
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The total absence of overtones would sound very boring to most of us. Listen to the sine wave (a tone that consists of a single, fundamental frequency, 440 Hz in this instance, with no overtones) at the following site: http://www.hark.com/clips/ytxtclfjjg...onds-12db-loop
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Yours truly, Dave Morefield A veteran is someone who at one point in his or her life wrote a blank check made payable to 'The United States of America' for an amount of 'up to and including my life.' |
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PC's mention of overdriving the top reminds me of another point, which I hope someone can state more clearly than I'm about to.
So far we've been discussing what I'll call predictable harmonics, for want of a better term. However, long ago in engineering school I [barely] learned how to analyze the effects of distortion, for example a sine wave with the bottom and the top clipped or rendered flat rather than curved (when represented as a graph of amplitude versus time). It turns out that any periodic waveform, no matter how un-sine wave, can be mathematically represented as a series of sine waves, all of which are harmonics of the fundamental, of various amplitudes. If one plucks a guitar string hard enough, I presume that the above effect takes place. If so, it would be an instance where overtones, at least some of them, cause the sound to be unpleasant to our ears. I just now found some more frequency synthesis magic: http://www.rhythmcreation.com/2007/1...sawtooth-waves The sine wave consists solely of the fundamental frequency. The other three are combinations of the fundamental plus harmonics or overtones.
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Yours truly, Dave Morefield A veteran is someone who at one point in his or her life wrote a blank check made payable to 'The United States of America' for an amount of 'up to and including my life.' Last edited by bluesbassdad; 10-12-2011 at 02:03 PM. Reason: magic |