[PD] Smooth looping

[Matt Barber]

> On Sat, Apr 24, 2010 at 11:32:52AM +0200, Roman Haefeli wrote:
>> The fact, that old Pd "rabbits" like you also have questions not only
>> answers, is comforting.  (even if they turn out to be not real questions ;-)
>
> The more you learn, the more questions turn up. :)
>
> Anyway back to the looping: With the fix, I can smoothly loop sine-waves now,
> but it still is pretty hard to get good looppoints for samples.
>
> Here's an example soundfile: http://footils.org/snd/23.wav
>
> With loopstart for example at sample 2912 and loopend at 5402, this looks
> pretty even in the array overlay, but if you listen to it, you can still hear a
> nasty rumble. I wonder, how to get rid of this ...


I don't do very much looping, but if intuition serves I think you need
to find loop points that share both the same value and the same first
derivative (if your source is more or less periodic you can think of
this as looping several sine waves and then mixing the results, and
though I haven't thought it through it seems like the value and
derivative would match best in places where the phase is similar for
each constituent at the loop points).  When I've tried to do looping,
I've found it a little easier to find peaks with similar values,
because I know that the derivative is the same at those peaks, while
it's much harder to estimate the rate of change on zero-crossings.
Anyway, for the sample you posted the best loop-point I could find was
2931-6153.

Matt