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Callan:
All other things being equal, the main thing that effects the
"clarity" of a sonograms produced digitally is the scaling process
that is used to convert amplitudes (or the power measured at each
frequency) into colored (or gray scale) pixels. I think of this as
adjusting the contrast in a picture. Indeed, one of the things you
could try is generate a sonogram, save it as a graphics file (.png or
.jpg, say) and edit it with a photo editor. I suspect that, as you
increase the contrast of the picture, you'll think the sonogram gets
clearer. If this is the case, then probably what you want is a
sonogram program that lets you adjust the scaling of amplitudes to
pixel colors. If not, then what you mean by clarity isn't what I think
you mean and I haven't got any useful suggestions for you.
I draw most of my sonograms (you can view some from files linked unde
rthe examples section at http://math.uc.edu/~pelikan/Dora/) with a
program (the java program Dora also linked from that site) I wrote
that allows the user to specify arbitrary scalings. If I set the
scaling to completely ignore all the low amplitudes and only plot the
highest 25 or 35% of them I get pictures that look a lot like the old
Kay spectrographs --- most background noise and most overtones
disappear. Of course, this clarity comes about because I'm throwing
away information and that's something I always worry a lot before doing.
Cheers!
Steve P
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