[MPlayer-dev-eng] [PATCH] audio filter volnorm2 - two-pass audio normalizer

[Zoltan Hidvegi]

Ivan Kalvachev wrote:
> > Explanation:
> > AC3 5.1 sound on DVDs is usually not loud enough
> > and needs aplification. There is number of ways to make
> > it louder
> > (like -af volume or encoder gain), but you must either
> > guess gain value
> 
> Have you tried -a52drc option?

AC3 is not quiet because of DRC, it is quiet, because downmixing from
5.1 to 2.0 in liba52 lowers the volume too much, probably because it
is based on the assumption that all channels are equally loud, but in
fact most of the time only the front channels has real action (and
very often only the center channel).  But if liba52 did not lower the
volume, than it would have to clip when all channels engage in full
blast.  The problem is that the low volume audio is resampled from
float to 16-bit which loses precision, so use -af-adv force=4 or 5 if
you plan to increase the volume.

Zoli