This is the area in which I grilled the MS Audio Encoder because I
got the most tangibly interesting results from it:
Notice how in the 5 & 12 kbps samples the high and the low tone toggle
between eachother, unsure of which should take dominance. Also note the
frequency cutoff (the high tone suddenly appears & disappears): oddly
enough, this cutoff is not at 4khz as we might expect, but considerably
lower. The warbling would seem to indicate the encoder is using a sort of
"point of focus," where it concentrates on the most energetic portion of
the signal. The lower-than-4khz cutoff seems to also indicate that this
focus model is not based on filterbanks, or at least a very different
model. This is clearly something entirely different from the MPEG-type
perceptual audio encoders. Listen to these MP3 files and hear how the
high tone reaches a full 4khz before cutting out:
One thing that amused me about this bank of MP3s is that RealAudio's
builtin MP3 decoder was unable to render them properly, but WinAMP
had no problem with them! Clearly, there is some variation in MP3
decoder implementations! To their credit, the Xing, Sonique, and
FreeAMP players were all able to successfully play both sets of
files. Note how the MP3s properly cut off at 4khz.
Again, the G2 test did not provide any
interesting result, due to the limitations on the free version of
their encoder. (The paid version costs $150!) The 20kbps stereo
encoding performed adequately.
