Microsoft Audio Codec 1 at 160kb/s

 

MP3HQ128k.gif (4316 bytes)
160kb/s ASF Frequency Response

MP3HQ128kS.gif (40941 bytes)
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 file.

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.

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1999 Peter Miller for MP3'Tech - www.mp3tech.org