Doppler effect vibrato?

[gusl]

http://bottom-end.blogspot.com/2006/05/bernoulli-doppler-and-natural-vibrato.html

Gustavo Lacerda said...

I doubt the Doppler effect in your throat could be strong enough to be noticeable. For the first frequency doubling (octave), you'd need the sound source to be moving at half the speed of sound (i.e. v = 1/2 c). To triple the frequency (i.e. lambda = 3), you'd need it to move at 2/3 the speed of sound. In general, 1/lambda = 1-v/c, or v = c (1 - 1/lambda).

If we take the minimal noticeable change to be 20 cents (where 1200 is an octave), lambda = 1220/1200 = 61/60.
Thus v = c (1/61) = 1/61*340m/s ~= 5.57 m/s .

I don't think throats reach that speed when they vibrate.

I found that post by googling for Doppler effect + vibrato, because it's a cool idea.

Comments

[zarex.livejournal.com]

You're right, this guy doesn't know what he's talking about. For Doppler to operate, there has to be relative motion between the source and listener. For Doppler to cause vibrato, this relative motion has to be periodic. Not gonna happen.

[gustavolacerda.livejournal.com]

Well, my throat does vibrate periodically when I sing, which causes said relative acceleration. But this motion is producing the note itself, rather than a wavering of the note.

[gustavolacerda.livejournal.com]

I guess sound sources are never completely stationary.
If you were shaking your head as your sang, a less tiny Doppler effect would occur.

[zarex.livejournal.com]

Sound sources vibrate, but they need not "traverse" relative to the listener. Shaking your head would be undetectable, and basically zero Doppler, for all intents and purposes, since you need to move relative to the listener. You might get a little tremolo from the change of amplitude/frequency content with altered direction, though.

[zarex.livejournal.com]

Right, but that's something completely different from the Doppler effect, and there is no "said" relative acceleration. Vibrato is just a periodic modulation of the tension of the vibrating system (vocal chords). The vibration itself doesn't use the Doppler effect at all.