[vorbis] joint stereo - advantages / when?

[Monty]

> I've been postponing some of my encoding for when joint stereo gets
> implemented. The reason I've been doing this, is that I am under the
> impression this is the largest step in the quality/bitrate ratio that's
> left. Now I'm wondering if I am correct in thinking this. lame's
> documentation seems to imply it doesn't make much of a difference at
> higher than 128kbps (I quote: "To disable joint stereo encoding
> (slightly faster, but less quality at bitrates <= 128 kbps)"), but this
> could just be because one anyway doesn't hear much of a difference
> between 128 and 160 kbps?

The problem with joint stereo is that the perceptual qualities of the
two encodings can sound very different, and if the selection algorithm
makes a mistake...

It may also be the case that you also may not notice a quality
difference between the two modes (L/R or mid-side), but you would
notice the transition from one mode to the other.

Because the selection algorithm is not perfect, at higher bitrates,
LAME turns joint stereo off by default.

> Secondly, this feature doesn't _appear_ to be too high on the priority
> list. (Or is it just technically a lot more difficult than the other
> features?) I know this is supposed to be in Vorbis 1.0, which should be
> released before the end of the year. Is it likely that we will have to
> wait until nearly 1.0 for jstereo, or are there plans to implement it
> within, say, the next two beta's? (And are there any dates attached to
> this? I suppose not.)

b3 will not have it (yes, it's somewhat more difficult than other
features).  b4 *will* have it.

Monty

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