Klarinet Archive - Posting 000234.txt from 2001/02

From: Richard Bush <rbushidioglot@-----.com>
Subj: Re: [kl] Organs and combination tones
Date: Wed, 7 Feb 2001 22:15:08 -0500

Sorry William for this short note. I just don't have more time at this time.

Difference tones do exist and are audible products of two different sounding
pitches sounded at the same time. We could go on an argue about whether the
falling tree in the forest makes a sound if no one is there to hear it, but
I, like you have never solved that problem.

Difference tones are NOT a mental phenomenon.

William Wright wrote:

> <><> I wrote:
> So far as I know, the word "hear" is very important because (so far as I
> have read) a difference tone is manufactured by flesh in the human ear,
> not by interference or summation of sound waves outside of the ear. (See
> Arthur Benade, "Horns, Strings, and Harmony", Chapter IV, pg. 80+ in the
> Dover paperback edition.)
>
> <><> Somebody else wrote:
> You may be misreading Benade or something [snip] A difference tone
> does not need to be manufactured; it exists in the air, as surely as two
> pebbles dropped in a pond will cause interfering waves in the water.
>
> Tony Pay has cited a reference besides the one that I cited, and I'm
> pretty sure that this is a clear-cut issue:
>
> A 'difference tone' does not exist outside the person's ear,
> whereas the 'beat' produced by two mismatched notes does exist outside
> the ear.
>
> A 'difference tone' is manufactured inside the ear because tissue
> inside the ear begins to vibrate at a frequency other than any of the
> incoming components. This vibration is translated to electric
> discharges and processed by our brain, and hence we 'hear' something
> that doesn't exist outside the ear.
>
> Is it disturbing to think that we hear things that don't exist?
> It disturbs me, that's for sure, but measuring instruments say that it's
> true. Over the last year, thanks partly to conversation here and
> partly to reading --- "Maestro, I read" --- "Oh you! You need to
> practice more" --- I've had to change (reluctantly) my thought process
> about such things.
> I've read about an optical illusion that is based on similar
> principles (manufactured perception rather than simply ambiguous input).
> In this illusion, a neurologist claimed that I would see a piece of
> paper rise up from the floor, float on edge in mid-air and dance
> non-stop for me. This was a little bit too much for me to believe
> ..... until I tried it!
>
> ....anyway, the confusion between 'difference tone' and
> 'interference' is this: When two waves add (or subtract), they are
> merely combining their amplitudes to create larger and smaller
> amplitudes as they drift 'into phase' and then 'out of phase'. They
> are not creating a new frequency component. They are only reinforcing
> or cancelling existing peaks and valleys.
> When we hear the rise and fall of amplitude (fluctuating loudness),
> we say that we hear a 'beat'; but this is only a change in volume or
> loudness, not a new frequency component. So long as the two
> frequencies are close enough together, we don't believe that we hear a
> new frequency, only a rising and falling volume. And when the
> frequencies *do* get far enough apart, then we begin to hear separate
> notes (perhaps in harmony or discord) and the sensation of 'beat' begins
> to fade.
>
> What does this have to do with the reading on a tuner? Not much
> except that unless some part of the tuner responds in the same way as
> the ear does, then something else besides 'difference tone' is happening
> that accounts for the discrepancies that someone asked about in the
> beginning of this thread.
>
> Cheers,
> Bill
>
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