Steve:
I'm not a physiologist, but I am familiar with research that shows human
hearing is octave-based, more or less. In other words, our ability to
discriminate slight frequency differences correspond closely to an octave
model, at least through the midrange of human hearing.
If sonograms are presented as an intuitive picture of sounds, then the
vertical frequency axis should show a doubling of frequencies. The
arithmetic scale is very misleading in this respect because it severely
"compresses" low pitched sounds and severely "expands" high pitched sounds
in the frequency dimension. This creates a misleading picture and makes high
pitched bird songs look as if they are much more frequency variable than
they actually sound to the human ear.
As I understand it, FFT analyses are not at all based on the physiology of
human hearing. FFTs are based on constant bandwidth analysis. In other
words, if the analysis bandwidth that's chosen is, let's say 50 Hz, then
equal emphasis would be given to analysis of a full octave at 50-100 Hz as
would be given to a tiny fraction of an octave at 10,000-10,050 Hz. And the
arithmetic sonogram reflects this bias. This has little relationship to the
way we hear or the way birds hear. It is simply the result of constant
bandwidth analysis. It is a mathematical constraint.
If scientists want the most biologically significant analysis of bird songs,
then the analysis bandwidth should be varied through the frequency domain
based on actual physiological measurements of frequency discrimination
ability in the birds themselves.
Lang
Lang:
There is really only one logarithm function; log2, loge, and log10 are all
proportional --- constant multiples of each other.
Consequently, any log plot looks exactly like any other log plot. The only
difference is the actual
numbers that appear labeling the vertical axes. So what you're asking for is
a log plot with labels
obtained by doubling. (In the program, the log is probably computed with the
natural log, since that is
the only log many computer languages provide.)
I agree with you that the labels should probably be something like
C,C1,C2,C3..., meaning the
labels should represent doubling of frequencies, and probably the exact
frequencies of notes on a musical scale,
since that is what many of us are trained to "hear" in our heads. (Whether A
is 440, 424, etc. is something else
people could argue about depending on whether they're old music fans or not
:-))
But this is a matter of choice and training. The log scale used in reporting
sound intensity as dB seems to have a
a fundamental justification based on the physiology of hearing.
Didn't the old "Golden Guide" to birds --- the one with sonograms --- have
a picture in which the frequencies
are labeld with notes of the musical scale?
Steve P
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>From Tue Mar 8 18:23:28 2005
Message: 2
Date: Thu, 13 Mar 2003 07:42:01 -0700
From: Doug Von Gausig <>
Subject: Re: Sound editing & sonogram software on PC
At 08:33 PM 3/12/2003, Walt wrote:
>Doug Von Gausig wrote:
>
>What I'm asking about has nothing to do with dB range. It's the FFT
>Blocksize. I may be mistaken about what CoolEdit means by bands. And the
>math behind a sonogram is something I have only a very basic understanding.
What CoolEdit means by "Bands" is the number of vertical "slices" that make
up the screen picture - you can zoom in to whatever sample length you want
and it will be drawn with the resolution you set in CoolEdit's spectral
settings menu. I use 256 or 512, as that's the best picture for me, and
doesn't take long for my tired 500MHz processor to draw.
Doug
Doug Von Gausig
Clarkdale, Arizona, USA
Moderator
Nature Recordists e-mail group
http://groups.yahoo.com/group/naturerecordists
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