ALSA: How to reverse LFE and Center Channels (5.1 sound)

conn-fused · 11-07-2007, 08:59 AM

Using ALSA, how can I reverse the LFE and Center channels? I am using a 3 jack onboard sound system (VIA 8237 AC97), so both LFE and Center are being handled by what is normally the Mic jack. Unfortunately, what should be going to the centre speaker is going to LFE (and I presume the reverse is also true) when I run a command like:

Code:

mplayer -channels 6 -ao alsa:device=surround51 chan-id.ogg

The speakers I'm using (X-530s) are set up in such a way that I can't change the wires to reverse the sound (at least externally!), so I need a way to do it at a software level. I can't seem to find an appropriate, obvious option in kmixer or alsamixer, however. Nor in the aRts controls (I'm running KDE & arts on top of ALSA)

Thanks!

conn-fused · 11-12-2007, 12:18 AM

Hi all,

Thanks for looking in on this thread. Although I still don't know why this soundcard and speaker set requires me to reverse the center and LFE channels, I've found a way to do it. Just make a ~/.asoundrc file like this:

Code:

pcm.surround51         pcm.surround51fix

pcm.surround51fix {
    type         route
    slave.pcm    "cards.pcm.surround51"
    ttable.0.0   1
    ttable.1.1   1
    ttable.2.2   1
    ttable.3.3   1
    ttable.4.5   1
    ttable.5.4   1
}

The first line aliases the surround51fix device to surround51, so that surround51fix is used whenever surround51 is called. The rest defines the routing and, as you can see, I've reversed 4 and 5, while leaving 0 through 3 alone.

There is a system wide equivalent to .asoundrc. I'm sure the changes could be put there if desired.

Hope that helps someone!