[MPlayer-advusers] liba52 downmixing

[Corey Hickey]

Jan Knutar wrote:
> On Saturday 03 September 2005 07:28, Corey Hickey wrote:
> 
>>I'm trying to figure out what happens to the lfe channel of AC3 5.1
>>audio when liba52 is requested to downmix. Is the lfe discarded? Is it
>>mixed with the remaining channels? Is it reduced and then mixed?
> 
> 
> Supposedly the lfe is so low frequency that it is dangerous to
> pump it to regular speakers, they could be destroyed.

I suppose low-frequency high-amplitude audio could be damaging to normal
speakers but from what I've heard from the several tracks I've tested
the worst it gets is a bit distorted. I'm testing with a pair of
Sennheiser HD 457 headphones (nice, but not high-end) and a JVC MX-77M
mini stereo system (probably better than any 2-piece computer speaker
setup, but not as good as a standard living-room stereo).

In fact, playing Terminator 3 with "-channels 6 -af
pan=6:1:0:1:0:0.5:0.7:0:1:0:1:0.5:0.7" sounds much more impressive on my
mini stereo than "-channels 2".

If anybody reads this and kills their $5 speakers don't blame me. :)

> I once wondered about the lfe too and extracted the track from a few
> DVDs and found that very few of mine actually had anything substantial
> in lfe.

It's silent much of the time but picks up for explosions, impacts,
engine noises, and ominous music. If a DVD doesn't have any of those
than you won't hear much out of the lfe. :)

I finally found a short scene in Terminator 3 with some quiet,
low-frequency music. I'm pretty sure now that the lfe channel is indeed
discarded. If nobody tells me otherwise by some time tomorrow I'm going
to assume that to be true and write it into my docs patch.

-Corey