Re: [xine-user] Xine and audio volume

[Siggi L. <lan...@fa...>]

Hi,

On Tue, 20 Feb 2001, Derrik Pates wrote:

> [low audio volume in xine]
> That's the way it is. The way DVDs are mastered (and apparently VCD/SVCD
> discs too), the audio is just plain lower volume. I've noticed that on
> every DVD player I've used - on my computer, MP3s, CD audio, etc., is
> ALWAYS louder than DVD/VCD audio (even in 'doze). Even on the set-top I
> bought this past weekend (a rather nice Pioneer with p-scan support), I
> see it.

Well, not quite true: The reason why the volume is so low is
downmixing: The AC3 Sound on most DVDs unpacks to five separate Audio
channels which have to be mixed to form a two channel
(stereo) signal. This is basically done like this:

left  =3D (left front + 0.5 center + left surround) / 2.5
right =3D (right front + 0.5 center + right surround) / 2.5

We have tried to be a bit sloppy about the division, but when we divide by
,eg, 1.5 only, sound overdrives with some DVDs. So it's a trade-off
between proper volume and sound quality (overdriving gives horrible
crackling noises).

However, we reduced the share of the surround channels, which gives
slightly louder volume, but less surround effect with Dolby Surround
decoders.

This code used to be in libac3/downmix.c. However, it seemed to have
vanished there (now done by rematrix.c? G=FCnter? Anyone??)=20

> Turn up the volume. Get an amp. That's about all you can do...

For now, that's right...
Maybe, we can add some compressor code (ie. low volume is amplified, or
rather less extenuated). Anyone is welcome to help out here ;-)

Regards,
=09Siggi