[mythtv-users] 7+1 audio with alsa, xine and 5+1 DVDs
paul.woodward at gmail.com
Sun Jun 5 20:32:44 UTC 2005
What you say is interesting and I had no idea it was possible. It's given
me an idea - my brother's A/V receiver has a 6ch stereo mode which basically
replicates replicates the front speakers to the rear and it sounds fantatic
for music. Is it possible to do something similar with alsa config?
On 6/5/05, Michael T. Dean <mtdean at thirdcontact.com> wrote:
> Franco wrote:
> >I have a 7+1 soundcard (Audigy 2 ZS Platinum Pro)
> >with 7+1 speakers connected.
> I'm understanding this to mean you're going directly from the sound card
> to the speakers with no A/V receiver in between.
> >Unfortunately, when I watch a 5+1 DVD using xine,
> >it is NOT upmixed to 7+1 so two speakers remain silent.
> Which is probably a good thing (keep reading)...
> >Should I change the configuration of xine or alsa
> >to get the desired effect (and, how do I do it?)
> You could "easily"* do this using ALSA's .asoundrc to specify a device
> using the route and plug plugins. Basically, with this approach, you
> would simply copy 2 channels to the silent speakers (i.e. copy left- and
> right-surround to left- and right-back, respectively). Then, set up
> xine to use this ALSA device for 5.1 soundtracks.
> Note that while doing this will keep those speakers from being silent,
> you may actually be harming the overall effect of the audio. The
> different channels in a 5.1 audio recording are used to convey position
> information using precise and complex timing of the sounds on each of
> the channels. If you "copy" channels to extra speakers, you will
> lose/destroy much of the intended effect (i.e. your position information
> will likely seem "washed out").
> Even trying to calculate the timing and audio information to add to the
> channels would not work (i.e. if you were able to come up with some
> incredibly complex read-ahead and isolation technology that allows you
> to identify movement using front and surround channels and create the
> appropriate audio information for the back channels, you would be
> inventing new information--which is likely imprecise and would
> definitely change the effect). Think of it like trying to print a
> 640x480 digital image in 10 x 8 in format--it won't look very good
> because you're inventing way too much information. IMHO, your best bet
> is to leave the speakers silent.
> For more information why it's better not to mess with the original, take
> a look at some of the A/V and home theater guides on the 'net and/or the
> requirements for THX certification. Both will give you an appreciation
> of the precision of the source audio.
> *It's easy to do once you know how. Figuring out how is where you'll
> spend the time. Check out the FAQ at http://alsa.opensrc.org/ for more
> info--especially http://alsa.opensrc.org/index.php?page=FAQ028 . Same
> ideas apply, but routing from 5.1 to 7.1 is more complex than from
> stereo to 5.1.
> >Actually, I'd like to upmix to 7+1 every kind of
> >audio source, but this seems to automaticaly happen
> >whith e.g. mythmusic (stereo music always becomes 7+1)
> >as well as mplayer when playing stereo videos...
> This is easy to do with stereo audio and doesn't detract from the effect
> (i.e. stereo has only imprecise position information embedded within
> it--generally only allowing the user to distinguish whether the source
> was on the left or right), so there's typically no harm in copying
> left/right channels to left/right back and/or left/right surround
> speakers. However, in truth, you would ideally reposition your speakers
> when changing from listening to music to listening to a 5.1 movie
> soundtrack. More info is available on the guides.
> mythtv-users mailing list
> mythtv-users at mythtv.org
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