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Re: [Phys-l] Harmonics vs Overtones



On 04/02/2009 07:29 AM, Quist, Oren wrote:
.... I have been told by people in music that although the ear
cannot hear above, say 20,000 Hz, the sound will be different if
those higher frequencies are there or not. Or, put another way, the
trained ear can sense the higher inaudible frequencies being present
or not. Anyone have experience, or knowledge in this area?

I can tell you that the auditory system is very complex and
tricky.

Frequency is not the whole story.

I guarantee you that things that are "inaudible" in one context
are audible in other contexts. Almost any question that is framed
in terms of frequencies being "present or not" is ill-posed,
because the auditory system is not a frequency analyzer. For
starters, parts of the system are sensitive to phase (not just
to frequency).

The auditory cortex takes in the signal and processes it in N
different ways in parallel. Speech, music, and echolocation
are all processed separately and differently. Echolocation is
obviously exceedingly sensitive to phase, and is best understood
in the time domain; you might not need to mention frequency at
all. For many decades speech recognition R&D was based on frequency
analysis, although there has always been plenty of evidence that
the phase was relevant, and lately time domain analysis has become
trendy. I don't know much about the role of phase in musical
sounds, but I would be astonished if it were not at least _sometimes_
perceptible.

I mention phase because any filter that chops out components at
one frequency (even an "inaudible" frequency) will mess with the
phase at all other frequencies. Hint: The filter is subject to
a Kramers-Kronig relation. So I would not be at all surprised
if the filter had a perceptible effect even if it were tuned to
an "inaudible" frequency.