[vorbis-dev] Spectral band replication

[Robert Voigt]

On Monday 14 May 2001 13:51, Jan.Tangring at et.se wrote:
> This seems to contradict, and with a margin, the current statement of
> Thomson multimedia. Thomson multimedia says MP3PRO 64 kbps sounds like MP3
> at 128 kbps. Thomson is marketing MP3PRO as a technology for doubling the
> capacity of portable MP-equipment.

I'll tell you how I would obtain to figures like this if I were a greedy 
inventor wanting to make as much money as possible. I would select some 
pieces of music where my new audio codec performs very well and do double 
blind tests with low quality equipment, and claim that this is the kind of 
equipment most people use for listening to compressed music (computer 
speakers, headphones that come bundled with mp3 players). Of course my test 
people won't hear the difference between 128kbps conventional and the shiny 
new codec at 64kbps. This is not the way to determine the performance of an 
audio codec, but it's ok for marketing purposes, because most people don't 
mind being told something that is not exactly true.
There have been some improvements in audio codecs since the original mp3 was 
released, but they are not as great that 64kbps could sound like 128kbps. 
What's more, mp3pro is supposed to be compatible with mp3. This limits 
improvements considerably. Not everything can be done like any good engineer 
would do them if he startet from scratch.

> Am I perhaps being naive?

No, because you're trying to determine a proper level of skepticism.

On Monday 14 May 2001 14:59, Jan.Tangring at et.se wrote:
> - Unfortunately your source is wrong in his assumtions, comments Lars
> Liljeryd on Robert Voigts statement.
>
> - We cannot see that there are inherent or future limitations in SBR
> when in comes to higher sound quality.
>
> Lars Liljeryd says he don't want to speculate on where lies the
> "sweet spot" of SBR.  He is not willing to supply further technical
> details on how SBR works.

What I said about the figures above applies here too. The only way to claim 
that 64kbps mp3 with SBR sounds as good as >100kbps mp3 is the above 
mentioned way. I'm not saying there's no improvement. I'm saying the 
improvement can't be that great. 
If that guy was a little more open about the internals of his invention I 
could estimate the performance better. I wonder why he's trying to keep it a 
secret. If it's patentet he has nothing to fear. Perhaps I could find out 
more by searching a patent database, but it's not worth the effort. We can't 
use it in Vorbis anyway, Vorbis is patent free.

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