[vorbis-dev] Low bitrate high-band coding...

Jean-Marc Valin valj01 at gel.usherb.ca
Mon Dec 4 21:26:53 PST 2000

OK, I have just finished quantizing my coefficients and the result is better
than I had expected... 345 bps for the whole 11-22 kHz band. The audio files are
still at ftp://freespeech.sourceforge.net/pub/freespeech/

bach10-diffquant.sw  : The high band is quantized with 8 bits/frame, thus 345
bach10-diffquant2.sw : I used shorter frames to get better results, 690 bps

In order to get these bitrates, I used differential vector quantization in the
cepstral domain. There are two things left to try:

1) Use intra-frame LPC interpolation (in the LSF domain)
2) Predict the high-band envelope from the LSP masking curve, and further reduce
the bit-rate

By the way, what I'm proposing here is probably not something that would go in
the 64 kbits/channel modes, but in a very low bitrate modes, when there are
(almost) no bits left for the high band.


Jean-Marc Valin
Universite de Sherbrooke - Genie Electrique
valj01 at gel.usherb.ca

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