[Portaudio] Portaudio & FFTW

Richard Dobson richard at rwdobson.com
Mon Feb 5 12:55:28 EST 2018

Short answer is Yes. I have done this (in part - the resynthesis stage) 
in the program "pvplay" which is part of the now open-source CDP system 
(https://github.com/ComposersDesktop/CDP7). Of course if you want to 
receive audio samples you would need to implement the analysis stage as 
well (See the streaming "pvs" opcodes in Csound, based on the same code, 
in turn based on Mark Dolson's original phase vocoder).

The approach is broadly the same whether for a GUI app or for a command 
line streaming player such as pvplay. Once you have your "basic" phase 
vocoder code working (which is an fft-based analysis/synthesis scheme), 
create a background thread to handle the processing, and a ring buffer 
to hold incoming and outgoing audio samples from/to the portaudio 
callback. My code offered the option to use FFTW 2.1. rather than the 
provided FFT implementation. Tim Goetze made some LADSPA plugins based 
on my original implementation, but updated to use FFTW 3 

If you just want to do classic FFT-based convolution, you don't need all 
the extra baggage of pvoc; but you will still need the 
background/foreground mechanism, as for any process incurring arbitrary 
block computation and latency.

Richard Dobson

On 05/02/2018 17:19, cristiano piatti wrote:
> Good morning,
> does anybody know how to implement a FFTW (www.fftw.org) streaming
> audio example ?,
> and can suggest me how to implement a canonical dft and/or fft on a
> streaming of audio samples ?
> Many thanks.
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