This information is 2 years old; so, it might be out of date.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:
