Arch Linux

purzel

Member

Registered: 2012-01-05

Posts: 54

Downmixing/Adjust from 5.1 to 'true' 2.1

Hi folks!

I've got my hands on a "Creative Sound Blaster X-Fi Surround 5.1 Pro USB" and now am trying to get the darn thing to work...

I'm using ALSA and pulseaudio, and by setting the USB-soundcard as fallback device in pavucontrol every sound gets played back nicely over the external speakers.

The trouble starts with downmixing however. As the soundcard has 6 channels I can play back 5.1 content nicely but my current setup includes only 2 front speakers and a subwoofer. As opposed to most systems my subwoofer receives its input from a separate LFE channel. So when playing a movie, I miss the the center and rear-speakers.
What I want to have, is mixing the rear and center channels into the front speakers and leaving the lfe(subwoofer) in peace.

What I get is either no LFE or no inclusion of rear & center..

by editing /etc/pulse/daemon.conf
and setting:

default-sample-channels = 3

I get no LFE but rear&center included as in a 5.1 to 2.0 downmix.

I know of the "enable-lfe-remixing" function but since my subwoofer hasn't got a low-pass filter (yet) this very bad. Also it's not an ideal solution even with a low-pass since only the content intended for LFE should be sent to the subwoofer (or at least give me the choice to do it).

When in pavucontrol, I can only select: Analog Stereo Output; Analog 4.1 Output, Analog 5.1 Output.
If there would be plugin or anything to do 2.1 output this would be great...

I'd be very thankful for your help!

cheers
purzel

P.s. although I know my way around audio-stuff I'm still new to (arch)linux so please don't take offence if my questions are stupid ;-)

brebs

Member

Registered: 2007-04-03

Posts: 3,742

Re: Downmixing/Adjust from 5.1 to 'true' 2.1

See downmix_51to20 in my ~/.asoundrc, then hopefully you can figure out the rest.

purzel

Member

Registered: 2012-01-05

Posts: 54

Re: Downmixing/Adjust from 5.1 to 'true' 2.1

Ok, thanks

I found a different workaround however that is less intrusive. By using mplayer with the following options:

af channels=6,pan=6:1:0:0:0:0:0:0:1:0:0:0:0:1:0:0:0:0:0:0:1:0:0:0:0:0.5:0.5:0:0:0:0:0:0:0:0:0:1,sub=100:5

the "pan" section will mix the rear left and the rear right into the front left and front right, the center at 50% into front left and right. Also the subwoofer channel will receive the LFE signal. sub=100:5 will now extract its signal from front left and front right, at a cutoff frequency of 100Hz.

cheers!