[vorbis] Beta3 impressions

[Aleksandar Dovnikovic]

I tested Vorbis encoder - beta3 version, and here are my thoughts:

- In comparison to beta2, subtle high-frequency artifacts seem to be gone
(though they were small in beta2). Good job there! :-)

- Velvet.wav also sounds better, but transparent quality is reached
at -b256+.

- Horn.wav still sounds very sucky, mode -b256 gives ~100kbps (this
is understandable because in this sample practically there are no sounds
above 5kHz) but the artifacts can be easily heard. Mode -b350 gives
~310kbps but still there is a difference (subtle though). I also noticed
that you get similar artifacts when you encode simple tones (like 440Hz or
1kHz), no matter what bitrate is used.

- The most occurring artifact in -b128,160,192 modes is pre-echo (-b256+
seems to be free from this curse). The leader in eliminating pre-echo is AAC
(Liquid Audio, Low Profile AAC), because even at ~128kbps stereo there is
very little or no pre-echo (Temporal Noise Shaping works very well
obviously).
In his interview to Slashdot, Monty said that wavelets will be used in
Vorbis (after version 1.0). I guess that wavelets will be able to eradicate
pre-echo more thoroughly ?

- There is also an improvement (from beta2) with gapless tracks, but small
clicks are still there (not often though). I guess the only 100% solution
is, like Monty said, to add a feature to the encoder so that encoder knows
that it should match the end of one file with the begging of another one.

Comments are welcomed. :-)

Greetings,
Aleksandar

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