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Re: two sine tones simultaneously within one critical band

On 5 Oct 2005 at 16:54, Martin Braun wrote:

> Jan Schnupp wrote:
> > If you play two sine tones simultaneously within one critical band, then
> > the tones will interfere. Alternating constructive and destructive
> > interference will cause an amplitude modulation known as "beating". They
> > will be perceived as a single tone that "warbles" or "flutters" at a
> > frequency equal to the frequency difference. That's just physics.
> Physics, yes. But the "beating" effect has nothing to do with the critical
> band (CB). You hear a "beating", if the two tones are separated by a small
> frequency difference (up to ca. 15-20 Hz). If the frequency difference is
> larger than this, the "beating" effect disappears and you hear two tones in
> dissonance.

Not to put too fine a point on this, but it's only "physics" if there is some
nonlinearity in the system.  Two sine waves, added linearly, contain no
extra "beat" components... even though beats seem to be clearly visible
in the waveform.  What really happens is that there are peaks in the
total waveform which occur at the beat frequency.  If such a wave
passes through a nonlinear system, then beat frequencies are generated as
real tones.   One might suppose that given the known nonlinearities
in the peripheral auditory system, this might be the explanation of the
beat phenomenon.  However, I seem to recall that there is evidence
against this explanation... I just don't recall what it was, nor how
compelling it was.  Anyone?

Best regards,

Bob Masta