NForce4 AC3 Pass Through

[publicmsu]

Has anyone managed to get AC3 passthrough working with the alsa drivers in linux? I try using the -ac hwac3 with mplayer, but I hear nothing from my receiver. Is there something that i'm doing incorrectly?

[asdere]

Originally Posted by publicmsu

Has anyone managed to get AC3 passthrough working with the alsa drivers in linux? I try using the -ac hwac3 with mplayer, but I hear nothing from my receiver. Is there something that i'm doing incorrectly?

I assume you want spdif/coax digital output. You'll need to look around in /proc/asound/devices. Particularly, the digital sound playback. Use the device number for the -ao alsa:device=hw=0.2 (or whatever the device number is instead of 2).

[publicmsu]

I've got the stereo output working over spdif, however pass through does not work. I've tried using the -ao alsa:device=spdif (iec958, hw0.2), I've attempted all of the above and nothing but silence. I'm getting quite frustrated with this NForce offering, as it has the spdif output. Pass through works in windows, but not in linux. I've read posts indicating that it works with the OSS drivers that were provided by nvidia, but would rather stick with the alsa offering if possible, because I think the OSS solution was quite dated.

[publicmsu]

here is the output of my aplay -l:

**** List of PLAYBACK Hardware Devices ****
card 0: CK804 [NVidia CK804], device 0: Intel ICH [NVidia CK804]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: CK804 [NVidia CK804], device 2: Intel ICH - IEC958 [NVidia CK804 - IEC958]
Subdevices: 1/1
Subdevice #0: subdevice #0


when I try to execute the command mplayer -ao alsa:device=hw=0.2 -ac hwac3, it's silent. When I remove both of the audio command lines, I hear normal stereo audio. Is this chipset able to pass through the ac3 signal properly, or am I wasting my time trying to get this to work?

[Jason_25]

I would like to know the answer to this too. It works fine with the OSS drivers but with the more recent drivers you have to change the source for it to compile.

[asdere]

Try twiddling with the mixer settings.

/usr/bin/amixer set IEC958 off
/usr/bin/amixer set IEC958 on

And also alsamixer.

It is a bit 'wierd', sometimes I'd have to turn the IEC958 off and other times on. Or like the very first audio file comes out screetchy but subsequent audio is fine.

Also, try without any alsa.conf, .asoundrc etc. Go direct hardware naming (ie, hw=0.2). iec958 and spdif are aliases and may not be correct from the defaults.

I also use the comma with "mplayer -ac hwac3, " that should help with none ac-3 sound.

[publicmsu]

I've attempted nearly every combination known to man, and still have been unable to get any sort of AC3 pass through to work with this chipset. What is the big problem here? Things work just fine in windows, I can't believe that no one has addressed this issue in linux. This is a very popular chipset, and I would come to expect a feature like this to work without such a headache. I'm quite disappointed in the alsa solution at this time, and wish someone could offer some sort of solution!

[publicmsu]

Apparently the alsa drivers do not support AC3 pass through on the nforce4 chipsets? I've not found a solution anywhere, and no one has been able to suggest anything. Quite disappointing.

[J.F.]

I'm having the same problem... but I think the problem is in mplayer and xine.

aplay -Dspdif ~/music/dts/SURROUNDTEST_011212.wav

This works fine, the audio receiver showing dts data coming across the optical connection.

mplayer -ao alsa:device=spdif -afm hwac3 ~/music/dts/SURROUNDTEST_011212.wav

However doesn't play... it just prints "a52: CRC check failed!" repeatedly until the file ends.

mplayer -ao alsa:device=spdif ~/music/dts/SURROUNDTEST_011212.wav

Plays fine, with mplayer decoding the dts, downmixing it to stereo, then playing the stereo as PCM across the digital connection.

mplayer -aid 137 -ao alsa:device=spdif -afm hwac3 dvd://1

Plays the DVD... if the audio track selected is PCM, it plays across the spdif just fine. If it's ac3 or dts, the audio receiver says it's getting ac3 or dts, but there's no sound actually played. Given all of the above, I think it's clear the bug is in mplayer (and xine acts exactly the same).

[Wolfman [TWP]]

There's an option in Xine, under the Audio tab called "Speaker Arrangement", set it to "Pass Through", and you should hear multichannel audio 5.1 etc.. That's how I have it setup on my system, as I use a Creative Audigy 2 sound card, connected to a Creative 5.1 sound system with decoder (5.1 Dolby/DTS). May work with that card too..

Wolf

[J.F.]

Originally Posted by Wolfman [TWP]

There's an option in Xine, under the Audio tab called "Speaker Arrangement", set it to "Pass Through", and you should hear multichannel audio 5.1 etc.. That's how I have it setup on my system, as I use a Creative Audigy 2 sound card, connected to a Creative 5.1 sound system with decoder (5.1 Dolby/DTS). May work with that card too..

Wolf

I set that... same as mplayer, BUT!!!! I figured it out after noticing that aplay said the dts file was playing at 44100 Hz, but mplayer kept saying playing at 48000 Hz. The deal is, most of these new chipsets (nvidia, via, etc) only play data at 48000 Hz. Period. Most of these ac3 and dts data streams I've been trying want to play at 44100 Hz. aplay apparently handles that, but neither mplayer nor xine handle it. They stubbornly insist on trying to output at 48000 Hz. What you need to do is set up your .asoundrc file to use dmix to change that 48000 stream into 44100.

pcm.nforce-hw {
        type hw
        card 0
}
pcm.!default {
        type plug
        slave.pcm "nforce"
}
pcm.nforce {
        type dmix
        ipc_key 1234
        ipc_perm 0660
        slave {
                pcm "hw:0,1"
                period_time 0
                period_size 1024
                buffer_size 8192
                rate 44100
        }
}
ctl.nforce-hw {
        type hw
        card 0
}

That got it working for me. I now have no trouble playing dts or ac3 straight through to the receiver... and it sounds GREAT!

Note the line

pcm "hw:0,1"

Be sure to make that whatever your spdif device ID is. Then all you have to do is direct the audio stream to "nforce", like this

mplayer -aid 128 -ao alsa:device=nforce -afm hwac3 dvd://1

Hope that helps someone else!

[Wolfman [TWP]]

The Creative sound card is setup for 48000Hz (by Default) as well, yet I haven't had any problems playing any multichannel streams.. *shrug*

The .asoundrc file should work for the OP just fine.. It's quite similar to the Audigy 2 setup..

Wolf