Re: realtime altivec fft -- checking & performance
Re: realtime altivec fft -- checking & performance
- Subject: Re: realtime altivec fft -- checking & performance
- From: john <email@hidden>
- Date: Mon, 13 Jan 2003 19:13:23 +0000
Hi Brian,
For those interested, I have an Obj-C fft version of Apple's VelEng FFT
sample code (has scalar version also). It is definitely fast, though
not quite as fast as the one Urs pointed to, but it is easier to use.
-- John
Thanks to the v2 hint yesterday, I'm off and running with our vst
conversions. I'd be interested in hearing from anyone with a fft/ifft
loop in their AudioUnit about cpu usage in the realtime case. I was
getting 33% with old c code and now 20% with what I think is
Altivec-enhanced code on a Powerbook 1GHZ / 1GB. I say 'what I think
is' because I am not positive that the fft is being vectorized thanks
to doubts that our input data structure is 16-byte aligned. (We have to
interface with lapack/blas with our own vector class, but I've added
the __attribute__ ((aligned (16))) parameter to try to fix it.)
1) Is 20% "OK" for this sort of machine in realtime? My pIII 800 on VST
would get about this, so I'm wondering, especially since the g4 altivec
fft is highly touted.
2) Is there a way to make sure that the fft code is being vectorized?
The vDSP docs say that it will fall back to scalar if certain
parameters aren't met but don't suggest a way to check.
_______________________________________________
coreaudio-api mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/coreaudio-api
Do not post admin requests to the list. They will be ignored.