Re: Quality of CoreAudio SRC

On Jan 31, 2008, at 1:29 PM, Herbie Robinson wrote:

Bias published a paper on SRC about a year ago that included FFT analysis of frequency sweeps:

http://www.bias-inc.com/products/peakPro5/resampling/peakResamplingWhitePaper.pdf

This information is 2 years old; so, it might be out of date. Undoubtedly, the thresholds for the color assignments are chosen to make the Bias SRC look perfectly clean, but that doesn't make the information inaccurate. This has been widely publicized on some of the audio engineer e-mail reflectors and nobody has ever challenged it as being inaccurate. Unless somebody from Apple tells us otherwise, we can probably assume Logic is using the Core Audio SRC. Note that distortion components in that plot are getting into the green range, or -120db. There is also aliasing around -140db. My guess about this is that the Wavelab SRC is using single precision floating point for the MAC loop, the Logic SRC is using the Altivec MAC (which is a little better than single precision) and the really clean SRCs are using double precision for everything.

This information is two years old. Also, note that if one compares Intel vs PPC using Altivec, the result must be different, because the Altivec floating point MAC instruction is a unique beast that does 4 multiplies and 4 adds in double precision, but truncates the result to single precision -- Theoretically, that would be 12dB less roundoff error than straight single precision (but much much more than using full double precision).

Bias has published the Matlab scripts for generating the plots at:

http://www.bias-inc.com/products/peakPro5/resampling/

--
-*****************************************
** http://www.curbside-recording.com/ **
******************************************
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Coreaudio-api mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/coreaudio-api/email@hidden

This email sent to email@hidden

References:
	>Quality of CoreAudio SRC (From: Brian Willoughby <email@hidden>)
	>Re: Quality of CoreAudio SRC (From: Herbie Robinson <email@hidden>)