Autocorrelation functions, was Re: [PD-dev] using SIMD instructions in externals

[Ed Kelly]

> I don't understand your AMDF algorithm. Why do you
> overwrite temp0 in the 
> inner loop, discarding all previous accumulations of
> fabs ???

Whoops! After I posted that email I noticed the error.
The bizarre thing is that the voicing_detector~ seems
to work anyway! Maybe it will work better with the
bugfix. A SIMD version is in development...

> In any case, AMDF doesn't seem to be
> FFT-optimisable. Especially, the
> absolute value is difficult to get rid of. That
> doesn't mean that there
> isn't a O(n log n) trick to compute it though.

That's what I meant, and especially since this seems
to be the slowest procedure of the external code. The
formant estimator I'm porting has a similar
autocorrelation algorithm, so what I'm really asking
is whether it is possible to make a generalized radix
autocorrelation object/code.

> A degree in what exactly???... I'd rather use math
> books than math profs.

British self-deprecating humour for "I don't know
enough about this shit, and sorry if my questions are
a bit dumb" - but you're right, I need more books than
just Kernighan and Ritchie for this...

Best,
Ed

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