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In the radio world, using radio reflectors etc sized at
10% of the wavelength is regarded as precise enough for accurate
operation.
I wonder if, in hearing aids, using more "bands" each set
to say 10% or so of the critical band width would ensure "precise"
processing?
----- Original Message -----
Sent: Wednesday, September 28, 2005 9:20
AM
Subject: Re: Critical bands v hearing
loss
Jim is right to point out that things aren't as simple as that.
You could play a 100 Hz tone and a 110 Hz tone, but slightly offset their
interaural levels and their onsets, and they will be perceived as two separate
tones even though they fall into the same critical band. Or you can play a
100Hz tone and a 300Hz tone simultaneously with the same interaural level and
you will perceive only one tone (albeit a "complex", "harmonic" one) even
though you now excite two well separated critical bands. I wouldn't claim to
be an expert, but the impression I have is that, when it comes to auditory
scene segmentation, critical bands are not that critical. Or am I wrong
there?
Jan
beaucham wrote:
On Thu Sep 22 01:26:43 2005 Vinay S.N wrote:
The human ear can only make sense of one signal per critical band. For
example, if two sine tones of 100Hz and 110Hz are played, two distinct
tones are not heard. This is because the critical bandwidth at 100Hz is
about 80Hz, and the two tones would be within the same critical band; one
will only hear two distinct tones when the two excitations exist in
separate critical bands. Hence there is no point in having controllable
bands which are finer in resolution than a critical band.
I don't think this is true in general. If the tones are too close
together (less than 20 Hz) beats will be heard. Between 20 and 40 Hz
difference a roughness sensation is heard. Beyond that two tones can
be heard. Also, if there are three tones, the relative phases can be
aligned to imitate amplitude OR frequency modulation, and they sound
entirely different. The question is how much detail can be heard
within a critical band. The case I referred to in my previous note
was the harmonic spectrum case, which I neglected to mention.) I'm
sure this question has been explored, and I'd like to see some
discussion on this topic by people in the psychoacoustic area.
Jim
--
Dr Jan Schnupp
University Laboratory of Physiology
Parks Road - Oxford OX1 3PT
Tel +44-1865-272513
email: jan@xxxxxxxxxxxxxxxx
http://www.physiol.ox.ac.uk/~jan/
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