Re: pitch of unresolved harmonics

[Martin Braun <nombraun@xxxxxxxxxxxxxxx>]

Alex Galembo wrote:

> But "boring" bass tones consisting of several harmonics with equal
amplitudes produce pitch sensation. I think we just deal here with a
temporal rather than spectral perception.

Yes, this is correct. Here, only the final stage of the ordinary pitch
detector is assumed to be functional. The preceding spectral part is knocked
out, so to speak, by mutual inhibition of all pairs of adjacent harmonics.

These artificial bass tones, like many other artificial periodic sounds,
trigger the pitch mechanism of the brain via their envelope periodicity. How
this happens is still unknown. My working hypothesis is that delay coding
neurons in the cochlear nuclei (CN) and in the superior olivary nuclei
(SOC), which are part of the system of sound localization, transport
envelope periodicity up to the central nuclei of the inferior colliculi
(ICC). Here, any periodicity signal is then detected by tuned pitch neurons
in the same way as periodic signals from natural sound with spectrally
resolved harmonics. The obvious difference is that periodicity information
at the level of the ICC is much richer in the case natural sound with
spectrally resolved harmonics. This could explain why pitch from sound with
resolved harmonics is perceived faster and more reliably.


> And: I have not found any data on the critical bandwidth in the range
below 100 Hz.
>
> And a question:
> Does the contradiction between Zwicker and Moore data of a critical
bandwidth in the low frequency range suggests that the Zwicker data are
wrong?

Below 500 Hz, CB data are difficult to determine. Further, these low
frequency data are probably related to a different mechanism in the auditory
system than the mid-frequency CB data (0.5 to 5 kHz). The latter are related
to the laminar anatomy of the ICC, the former are not. The psychoacoustic,
anatomical, and physiological literature on this issue has been reviewed:

Braun, M.(1999) Auditory midbrain laminar structure appears adapted to f0
extraction: further evidence and implications of the double critical
bandwidth. Hear. Res. 129, 71-82.

Martin

-------------------------------------------
Martin Braun
Neuroscience of Music
S-671 95 Klassbol
Sweden
e-mail: nombraun@post.netlink.se
web site: http://hem.netlink.se/~sbe29751/home.htm
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