160kb/s ASF Frequency Response
160kb/s ASF Spectral View
Here we have the results of testing the Microsoft
Audio Codec version 1 at 160kb/s. In general the results are very
similar to the results for testing at 128kb/s with slight improvement.
The frequency response is faithfully reproduced up
to about 16kHz but is slightly suppressed above this.
The spectral graph also shows plenty of content right
up to 22kHz. You can see how some lower intensity content has been
pruned down to about 12kHz.
The spectral graph of the source material shows LESS
high frequency content above 20kHz than the ASF file. This would
indicate to me there are a lot of distortion components in the ASF
output signal. The situation is not quite as severe as in the 128kb/s
Comparing the bright vertical bars in the spectral
view where the trumpet notes are playing to the source material
graph is very revealing. You will see that the bars in the ASF file
are much broader than in the reference material's plot. There is
quite a lot of pre and post transient material being added. Again
the situation is not quite as bad as the 128kb/s file.
Listening tests also reveal the shortcomings of encoding
with this codec. The sound is slightly fuzzy and transients lack
definition. The valve noises from the trumpet are heard as clicks
and don't sound like the original at all. Stereo imaging is also
not well defined. The signal is definitely better than that in the
128kb/s version but MP3 encoding is definitely superior.