[vorbis] Coding technologies

[Jan.Tangring at et.se]

I made an interview yesterday with Lars Liljeryd of Coding 
technologies, the company defining MP3PRO, the new version of MP3 due 
to be released by Thompson in a demo version this summer.

I wonder if there is anyone on this list who can put what he told me 
in a bigger perspective? Several interesting issues came up, but most 
interesting of course is the method the company is using to add high 
frequency content to a narrow-band encoding.

Sorry, I don't know the details, cause Liljeryd wouldn't give the 
full story. And I didn't understand all he told me either ...

As I understood it SBR can be added to any of the music compression 
codings in use today. MP3PRO is SBR added to MP3 and AAC+ is SBR 
added to AAC. AAC+ is already being manufactured in silicon by some 
secret party.

Essentially as I understood it SBR guesses the high frequencies from 
the lower frequencies. This is an idea of Liljeryds dating back to 
about 1997.

-- Nobody had thought of the possibility of there being redundancy in 
the frequency domain, says Liljeryd.

- Could you, by analyzing the lower band recreate a higher band that 
looks about the same as the original?

-- I turned out to be possible, not in the technical, mathematical 
sense, but psychoacoustically.

I associated the reasoning to the exciter effect which used to be 
popular in recordings. And what do you know, Liljeryd has an old 
patent on an exciter. But on the other hand, he told med SBR has 
nothing to do with the exciter. On the other hand he says he thinks 
SBR could be used to build a very good exciter ...

Liljeryd has patents in the SBR area, but the way I understood it, 
also from the interview, patenting issues in this domain are muddy 
waters to say the least.

So I wonder, do other irrelevancy coding technologies work along the 
same lines as Coding technologies? Specifically Ogg vorbis of course, 
are you incorporating something SBR-like?

I got to listen to it and it sounded real nice -- though I am not a 
professional listener. Of course Coding technologies do make proper 
double blind listening tests with both professional and layman ears. 
And the pro's have OK:d it, so ... it works.


-- 
-- Jan Tangring, reporter Datateknik 3.0 (www.datateknik30.se)

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