🚀 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.