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Klarinet Archive - Posting 000316.txt from 2001/02

From: Grant Green <>
Subj: Re: [kl] Combination tones......
Date: Fri, 9 Feb 2001 15:22:55 -0500

At 07:40 PM 2/9/01 +0000, Tony wrote:
>This is a confusion of levels. Yes, the variation in amplitude is
>visible, as you say, on an oscilloscope and in the math. But it isn't
>*physically* there, because it doesn't 'waggle' anything real. The
>pressure wave itself is already doing that.

Please excuse me, but I don't exactly follow you. Are you saying that the
beating effect isn't "physical" because it is a variation of something that
is already varying? I'd say that the beats are as real as vibrato and
tremolo, which are periodic variations in sound (which in turn is a
periodic variation in air pressure). Periodic variation in air pressure
(within the hearing range) is perceived as sound, and a periodic variation
of either the rate (frequency) or amount of the pressure variation (volume
or amplitude) is perceived as vibrato or tremolo. They may only be
characteristics of the underlying sound, but I wouldn't consider that as
making them "non-physical."

>A 'waggle' in a concept like amplitude isn't perceivable by an eardrum
>-- it's already busy being waggled by something else: namely the forces

How can one *not* hear a variation in amplitude?

>You can see though, as I said in another thread, why the idea is
>attractive. In fact, it was put forward by Young in 1784, but
>contradicted by Helmholtz in 1877, who explained the picture outlined by
>George Kidder here.
>This true explanation of why we perceive a difference tone is actually
>much more suggestive, even though a bit difficult to approach.

Afraid I don't have a copy of Helmholtz handy (mine's at my office, while
I'm stuck at home today): is it possible to summarize his explanation?



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