I ran the tests that were published by the Bias engineers in their
white paper: http://bias-inc.com/products/peakPro...WhitePaper.pdf
and then applied them to all the combinations of OS's and
audio applications we use.
Without going into the actual math/params in the MATLAB files -
the goal is to test the sample rate conversion algorithm on
difficult conversions, e.g., non-integer conversion, e.g.,
downsampling (or upsampling). Depending upon how the code manipulates/scales
sample values mathematically, there can be different kinds of
errors introduced which result in noise and/or aliasing components, etc.
I tested with the source as
a sinusoidal sweep tone at 96K (24 bit), and then downsampled to
44.1K. A spectrogram is then run on the 44.1K (24 bit) downsampled
result, Using an exponential plot with a color map, an ideal sample
rate conversion shows a clean trace = a line for the audio spectrum
rising exponentially with frequency.
The white paper may explain this better, and you can see example
graphs there. But my understanding is -
all the signal energy should be concentrated only in the line trace for
converted samples, with no energy or frequency components above
or below it (the background of the rest of the plot should be the
darkest color corresponding to no energy/no signal). Think of
a bright red line (red = highest energy) representing all samples
perfectly converted looking like the curve rising from left to right
for the natural log, "e to the X", e^^X against a dark blue
background everywhere else (minimal energy or no signal). The
X-axis is time and the y-axis is frequency (increasing from bottom
For Logic 7.2 on an older version of Tiger, e.g., I think it was maybe
10.4.6 (Tiger) or thereabouts, - there was alot of energy outside
the trace for the converted samples (noise),
and also reflections of the curve representing
the frequency sweep (unwanted frequency components from sample
Listening to this result, you would not hear outright distortion, but
rather converted music would sound kind of muffled/fuzzy, and
laking in transparency. Depending upon your monitoring signal
chain, some people might not hear a marked difference (but we
did hear an obvious difference in blind A/B comparison tests
with Logic, B'Batch, Peak, etc.).
For Logic 7.2 on 10.4.10 (Tiger) there is improvement - but still some
unwanted frequency components (same for Logic 8).
But on 10.5 (Leopard), Logic 7.2 produces almost a completely clean
trace when doing the 96k to 44.1 downsample, and Logic8 actually
does a bit better. I'm not sure I can hear a difference between the
2 and Bias Peak 5.2 (which produces an absolutely clean trace).
So this is good news. We looked at buying B'Batch, but concluded
that for the money, Bias Peak was a better program.