[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
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http://claudiusmaximus.goto10.org
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