🚀 go-pugleaf

Sliding FFT's are useful for finding the varying frequency content 
of a signal as a function of time.  If the frequency content changes
slowly it is sufficient to slide several samples between FFT evaluations.
This is a hopping FFT.  A decade ago I use a hopping FFT as part of a 
speech spectrograph system.  The familiar 3D pictures of speech signal's
frequency content which look like mountain ranges are a typical application.
The longer the hop the less calculation needed, but time resolution is 
reduced.
 

I used the technique that William so succinctly described to track
blood flow in the uterine artery from ultrasound data in a study
at the University of Colorado.  Since the reflection of ultrasound
from a moving target produces a doppler effect, the spectrum of
frequencies recorded from the reflection of an artery gives a good
idea of the differing velocities of blood flow in the artery.

Arterial constriction and dyastolic and systolic blood flow could be
quite easily seen in the resulting sonogram.  I released the code
to the public domain.  You can find it in the edsnd package for the
NeXT at princeton.edu and sonata.cc.purdue.edu.

Steve

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 #  Steven M. Boker            #          "Two's bifurcation           #
 #  smb3u@virginia.edu         #           but three's chaotic"        #
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