Extreme audio stretching This tool (Paul's Extreme Sound Stretch) is able to produce extreme timestrech (50x, or even 100000x). Any song can become an interesting sound texture or ambient music (listen to this example).

The technique used is mentionned as:


  "spectral smoothing" the sounds.


How does an extreme time stretch algorithm work?

(it is opensource, I have studied it a bit, but I haven't been able to see a big picture of the algorithm yet)

I thought about :

sound input ====&gt;  STFT ===&gt; duplicate the frames 50x ===&gt; ISTFT ===&gt; output


but I'm really not sure about this.
Here is how the algorithm works:



So the steps are:

Input -> apply some window (hann in the frame) -> FFT -> Get amplitude > randomize the phase -> IFFT -> overlap and add -> out

Do it in a loop based in the strech Factor.

Paul wrote a Python code for all steps in this picture.