Newsgroups: comp.speech
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From: mkant+@cs.cmu.edu (Mark Kantrowitz)
Subject: computing speech spectrograms?
Message-ID: <C7K30K.LKu.1@cs.cmu.edu>
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Organization: School of Computer Science, Carnegie Mellon
Date: Tue, 25 May 1993 00:07:30 GMT
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I'm trying to write code to compute and display speech spectrograms, and am
getting wierd results. My code for displaying waveforms works fine, so
the problem is probably with my understanding of how to compute
spectrograms.

My input is ulaw-encoded speech files (captured using a mike attached
to a Sparc) which I've converted to linear. I pass 64 (or 128)
datapoints at a time to a FFT routine (shifting each time by 16
points), which returns 64 complex numbers. I interpret the magnitude
of the ith complex number as the intensity of the sr*i/64 Hz
frequency, where sr is the sampling rate. I plot only those
frequencies whose intensity is greater than some appropriate threshold
value. The resulting plots do not look like spectrograms.

Any suggestions?

--mark

