At 08:31 PM 3/17/02 -0500, you wrote:
>What FFT size are you using?
>
>Walt
>
The software does not tell me per se, for the creation, only for the FFT
size choice during the FFT file filtering sunctions. But I believe it can
be calculated from the "bands" number. I have always taken that to mean:
You take the total band width, from 0 to the Nyquist frequency (1/2 samping
rate) and divide it by the number of separate bands created for the linear
vertical display. So for 22050HZ, into 256 bands would be 86 Hz per band.
But no that you ask, I am more and more sure I am wrong, because the FFT
size tells how many samples are being used to form the local value for each
frequency band, true? When you open the Analyze -> Frequency window, which
draws a graph, y axis dB from 0 at the top to -120 (whatever you have to
Range set to) at the bottom, x axis left 0, right Fnyq. It allows you to
choose the FFT size - here now set to 4096, and filter Blackmann-Harris.
But back to the spectral display - color is a function of loudness, and as
you previously described it, as you reset the "bands" control from 128 to
4096, you of course see the vertical resolution going from coarse to very
fine. But you also seem to see the accuracy in the left-right (time
domain) resolution changing, so there is better time resolution for th 128
bands, and more horizontally spread out, poorer time resolution for the
more bands. This suggests to me Cool Edit is broadening the FFT size as
one demands more frequency accuracy, as there is a natural kind of
Uncertainty principle, here, you cannot know the exact frequency for a very
short time period.
I might find out more from the original Cool Edit author, which I will try.
my very best,
Marty Michener
MIST Software Associates
75 Hannah Drive, Hollis, NH 03049
coming soon : EnjoyBirds bird identification software.
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