State of 3D surround sound?

Guinpen · Guru Joined: 08 Dec 2004 Posts: 393

I was wondering whether Linux has any support whatsoever with 3D surround sound (5.1 or 7.1)? If yes, what cards are supported? How can that be configured? Any links, hints, or other information will be appreciated. My external Audigy 2 NX is the only thing keeping me from using Gentoo as my primary OS.

NeddySeagoon · Posted: Tue Mar 22, 2005 9:34 pm Post subject:

Godji,

Theres not much in the way of convertinfg stereo to surround but playing surround sound from DVD works.
Its just passthrough, so it should work with almost any hardware.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Guinpen · Guru Joined: 08 Dec 2004 Posts: 393

Could you point me to some HOWTOs or other documentation?

NeddySeagoon · Posted: Wed Mar 23, 2005 9:40 pm Post subject:

Godji,

Set up ALSA by following this guide http://www.gentoo.org/doc/en/alsa-guide.xml
If you use a 2.6 kernel be sure to use the ALSA kernel modules, not emerge alsa-drivers.

Configure Xine or Mpalyer, to use AC3 passthrough and surround just works from 5.1 sources.
The hard bit is getting ALSA set up.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Guinpen · Guru Joined: 08 Dec 2004 Posts: 393

Thanks!
I have three questions though, and if you could answer them, you're an ace

1. Why use the kernel modules (I use 2.6.11-love1 by the way). I currently have alsa-driver and sound works, and the giude recommends alsa-driver over kernel modules.
2. By sound works, I mean sound at 48000 Hz works. The Audigy 2 NX seems unable to properly play 41000. I read somewhere that the Windows driver secretly resamples to 48000, but it does so well enough. I currently use alsaplayer which has an option to resample; however, I'd love a more global solution to somehow make the ALSA driver do it, so that I can listen to other applications as well. Ideas?
3. The subwoofer, even in Windows, seems to ignore its own channel (in Windows where everything other than that functions as it should, dragging the subwoofer volume control has no effect), but listens to whatever is sent to the front speakers and plays that. In Linus where I only get sound from left front and right front, the subwoofer works. Any idea how to fix that small problem?

Finally, as weird as it is, checking the "Headphone" setting in gnome-alsamixer managed to upmix sound over the fron and side speakers (not the rear though). Generally, sound quality is lower than in Windows; I'm not sure why, but I think too much resampling is taking place.

NeddySeagoon · Posted: Wed Mar 23, 2005 11:23 pm Post subject:

Godji,

1. Unless the guild has changed is says use emerge alsa-drivers for 2.4 kerenls and use kernel modules for 2.6.
There have recently been a spate of posts regarding problems with alsa-drivers 1.0.8 and 2.6 kernels. You should only attempt that combination igf you have a bleeding edge sound card and may benefit from the the latest driver for it.

2. Surround Sound is sampled ar 48kHz and CDs at 44.1kHz. Yes resampling is required if you want to mix the two
There is a command line resampling app, that will do arbitary input and output sample rates (I forget its name just now). you could pike one stream through that to resample it to the other rate. The latency will probably be horrible though.

3. Some motherboards have the centre and sub-woofer transposed. They are wired incorrectly. I have an option in ALSA Mixer to Exchang Centre and LFE, which swaps them over.

To fix the quality issue, you need to play with the mixer settings. I find that with the PWM settting at 80%, noticable distortion sets in.
I suspect that its a digital scale factor difference between Windows and Linux, so can safely be ignored.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Guinpen · Guru Joined: 08 Dec 2004 Posts: 393

1. I see. I suppose Audigy 2 NX is not bleeding edge anymore.
2. If you can remember that program, I'd be really frateful. By your reply I assume the ALSA drivers themselves can't do it universally, right?
3. What do you mean by incorrectly wired motherboards. What does the motherboard have to do with it? I have an Intel ICH4-Mobile chipset, and the sound card connects through USB2.0. I'll play with the options, but I don't think I have such an option in the mixer.
4. For the quality issue, I also noticed distortion at high PCM values, even if overall volume was low. I'll keep playing with it.

Thanks a lot for your time!! I'm really grateful.

NeddySeagoon · Posted: Thu Mar 24, 2005 8:43 pm Post subject:

Godji,

1. I don't know the Audigy 2 NX.
2. I think the program I was referring to may be sox (emerge sox)
3.. I had missed that you have an external sound card, so it may not be relevant.
Some soundcards have the wiring to the Woofer/Centre jack swapped. This mixer option allows the channels be swapped in software.
4. PCM and Master control the volume in two different electrical places in the sound card. A reasonable setup can be obtained as follows.

Turn the master down to about 20%. Now play with PWM until distortion can be heard.
This is the maximum useable setting for PWM.
Do the same procedure with the controls swapped. The idea it to set one way below the distortion threshold while you play with the other, so you know which control has reached its useful limit.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.