[vorbis] Vorbis beta4 and -b256 mode quality

[Aleksandar Dovnikovic]

Hi.

Since I'm interested in quality, I did some listening tests using Vorbis
beta4, mode -b256. I think that ~256kbps, ~5.5:1 compression is
still a good tradeoff because I can put 6-7 albums on 1 CD-R
(assuming that the average length of an album is ~50 minutes) while
retaining excellent quality.

My comments:

1.) most songs are transparent but there are still some glitches that
appear occasionally (similar to glitch like in hf_glitch.wav that I sent
to Monty) - these are probably high frequency glitches because
they appear mostly with cymbals. Note however that these
artifacts are rather subtle so if you don't have some listening
experience you might not hear them at all. Still, in this bitrange,
these artifacts shouldn't be present.

2.) gapless song come out perfectly! - no more clicks and pops - this
is probably due to more accurate compression in beta4 so the edges
of the songs are now matching with no clicks and pops.

3.) there's still some pre-echo (castanets.wav and only one file from
my pre-echo test clips). But I think you're going to have a hard
time finding a song that will exhibit pre-echo in -b256 mode.

4.) horn.wav still doesn't sound transparent! -b256 gives 100kbps,
but there is still some noise introduced. It looks like VBR isn't
giving enough bits because MP3 doesn't have a problem with
this clip.

I'm only waiting for 1) and 4) to be fixed before I start encoding...

Greetings,
Aleksandar

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