� Hi everyone. I've made an observation with the versions of the Fraunhofer ACM codec
that I installed in about January some time & Lame 3.62. Yes, they're old versions, &
maybe a lot has changed since then, but... this is what I did-
� 1- Encoded a sample with moderately low stereo separation with both Fraunhofer &
Lame, to 22050Hz - 56kBit/sec - Joint Stereo.
� 2- Decoded with Fraunhofer.
� 3- Mixed to Mid/Side as PCM (manually) & compared the voiceprints.
� Lame's output appeared to just have the Side channel at a lower bitrate, with both
channels with a lowpass filter of 7756Hz (I think). Fraunhofer looked to be using a
much lower LPF for the Side (around 3.5 kHz?) than it was for the Mid (which was close
to full bandwidth).
� Is Fraunhofer's trick like the "Side channel starving" some of you were talking
about earlier? Well, whatever it is, I think it would be a great asset to Lame if the
user could set the filter of Mid & Side independently of each other, & independently
of encoding normal L/R frames at least until some good default settings are found
(that's if it hasn't already been implemented). We might be able to save a lot of bits
that way. All Lame should have to do is discard the high frequencies on the Side
channel before the FFT data goes through the masking algorithms.
� I haven't tried filtering Mid/Side separately before encoding yet... I might try
that later & see if it makes a difference with Lame.
� I know these filters are cheating, but MP3 in itself is cheating, right?
Shawn
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