On Thu, 4 Nov 1999, Robert Hegemann wrote:
> Greg Maxwell wrote:
> > The correct solution is not to remove the -2. :) We want that because we
> > know that the psy model is often too optimistic, as it really was designed
> > for CBR apps, and is thus more useful for choosing how to allocate bits
> > among subbands then for determining how good something actually sounds.
>
> No, that's what VBR quality selection is for, not the -2db thingy of tot_noise.
> If you want lame to lower the psy model thresholds about 2db, use -V5
> instead of -V6.
Currently VBR quality selection only select the number of subbands that
you permit to be over the psy model (unless I've drifted completely out of
sync from the codebase), this is a nearly useless metric.
> > The problem is that the psy models effectiveness for VBR selection use is
> > very veriable. Sometimes, it thinks there is a ton of masking when there
> > really isn't. Sometimes it's right on. The linear -2dB or the like really
> > isn't all that effective.
>
> And the linear -2dB permits lame switching to 32kbits on digital silence,
> when there is absolutely no energy in, forcing always to select max_bitrate.
I dont follow this statement. Can you please clarify?
> I don't see any chance of speeding up VBR encoding in doing so. You would
> still have the binary search to get the optimal bits needed, but for
> ath only mode.
Yes, I'm stupid. :) We only need to compute the threshold once.
> Have you had this 'why the hell did you choose 32K for this *$*@$ frame?!?'
> situation in recent lame versions?!?
No. I havn't kept up with recent versions because I've been working on the
ability to control bitrate within a window, and other projects.
[use ath]
> I'm afraid you would be always too pessimistic in doing so, or you would
> introduce distortions you don't want.
I dont know that I really agree. I hacked the code a while back to skip
the bitrate search, and pull the target bitrates from a file. I generated
a bitrate file by looking at the unquanted mdct and guessing. I got much
better results then -v0.
> I like the way VBR works now. OK it's slow, and there may be some BUGs still
> in there, but it's quite useable.
I need to try the newer code, but I found the older code disappointing.
Generally, if set loosely the files were smaller but it made wrong choices
(like going to low bitrates at the begings of words in speech causing very
bad distortion), or if set strongly, it wasn't worth it.
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