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Old 01-29-2005, 01:25 PM   #1
DGrierson
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LFE through center speaker, Philips PSC605 (CM8738 Rev 10)


Hi

Hopefully someone can help me
I've recently installed Suse 9.1 (kernel 2.6.5-7) and have been trying to get 5.1 support working on my Phillips PSC 605 soundcard. lspci reports the card as "0000:00:09.0 Multimedia audio controller: C-Media Electronics Inc CM8738 (rev 10)".

I can get the front, rear and LFE channels to work ok (they output whatever XMMS is playing, which is all I want really) using KMix but my problem is that the LFE channel is also being routed to my centre speaker (which is on the same jack, but a different channel). This is causing noticable distortion (crackling, speaker vibrating excessively) because the centre speaker is too small to drive the frequencies it is recieving.

I'm worried this might damage my speaker and I read there might be a way to configure ALSA to either reroute the centre channel like a "phantom centre" through the front speakers, or to completely disable the centre channel. I'm almost totally new to this and the mass of options available to put in the alsa.conf file seems mind boggling to me.

I would simply unplug my center speaker, but since it contains the volume controls and when disconnected, turns off the subwoofer, this isn't really an option.

Any ideas?

Much Appreciated

David

Last edited by DGrierson; 01-29-2005 at 01:27 PM.
 
Old 01-29-2005, 02:15 PM   #2
GregLee
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The alsamixer program might work better than KMix, so maybe kill KMix and try alsamixer.

Of course, LFE should not go to the center, so there's something wrong. The Alsa utility program speaker-test is useful to check that the correct channels are going to your six speakers.
 
Old 01-29-2005, 03:38 PM   #3
DGrierson
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Thanks for the reply Greg;

I couldn't get speaker-test to compile correctly but alsamixer gave me a clue as to the problem. According to my soundcard manual, and the windows drivers, I should have the LFE/Centre plugged into the Line-In socket, as I did. This worked fine in windows. The option in alsamixer was "Line-In as bass", which explains why I only got bass via that channel in linux. There was another option in alsamixer, "Mic as Centre/LFE". I tried plugging into the mic socket, and voila, proper sounds through the proper speakers.

This leaves me with a slight problem however; I now have to change my cables everytime I reboot into windows (mainly for DVD and gaming). This isn't a big hassle but the PC is awkward to reach. I think the easiest solution would just be for me to get a splitter cable and have the subwoofer plugged into both the line and the mic at the same time. Any "software" (linux based) solutions to this would be appreciated however.


Thanks,

David
 
Old 01-29-2005, 05:51 PM   #4
GregLee
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It's quite possible you could set up a .asoundrc file to reroute things, somehow. But I can't help, since I don't understand .asoundrc files very well. There is some info at the Alsa wiki:
http://alsa.opensrc.org/index.php?page=AlsaOpensrcOrg
:
 
  


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