[pd] hanning window + fft

Claude Heiland-Allen claudiusmaximus at goto10.org
Mon Sep 4 16:13:07 CEST 2006


mami music wrote:
> Hi everyone.
> Im starting to study the fast fourier transform. i´ve seen the patches 
> in the examples that come in PD. I have two quesions: I see and 
> understand what the Hanning window does. But why is ti necesary?

The DFT (and FFT implementation thereof) assumes each block is a 
periodic waveform with period=blocksize that continues forever in both 
directions.

In general the signal will contain components that don't fit that period 
exactly, so when they repeat you get glitches (unwanted frequencies).

So, you window to make the signal go to zero at both ends of the block 
so that it loops without glitches, but that loses information from the 
ends of the block, so you then overlap blocks to spread the losses 
between blocks, so on average you lose no information.


Has anyone made an example patch that explains this?  Something like a 
simple FFT filter with switchable windows, so you can hear the difference?


Claude
-- 
http://claudiusmaximus.goto10.org





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