--EDIT(alien): I just went through trying some things with alsa and learned more than I planned to about it. I have put a quick summary of getting it working in R5 here. The original page is still below.

Before you start, turn off "AC3 Passthrough" and "Use Mythtv volume controles". More on that later.

Quick and Dirty

How to find the output device for digital audio to put in the setup.

1. cat /proc/asound/pcm This lists the audio devices. Card 0 device 0 is usually analog, and the device /dev/dsp is already pointing to it. You can use /dev/dsp to access this device. Card 0 device 1 may be the digitial device. /dev/adsp is already pointing to it. You can use /dev/adsp to access it. If you are really lucky, you are done.

2. For nforce cards, the digitial out is card 0, device 2. You can use ALSA:hw:0,2 for your output device for digital. Similarly, RealTek? ALC655 uses card 0, device 4. You can use ALSA:hw:0,4. Check the output of the pcm file above and you can probably figure out where your digital device is.

Changing /dev/adsp

You may not want to use ALSA:hw:0,2 directly. You can change the /dev/adsp to point to something other than hw0,1 by editing /etc/modprobe.d/alsa-base and adding the following line:

options snd-pcm-oss adsp_map=2

Then from the command line:

update-modules
depmod -a

Followed by a reboot. /dev/adsp will now point to hw:0,2.

Using asound.conf

You can create an /etc/asound.conf as described on this excellent Digital Sound HOWTO page. This will create an alias ALSA:digital which is the same as ALSA:hw:0,2 above. Make sure that asound.conf is readable by mythtv (chmod a+r /etc/asound.conf).

It will also create an ALSA:mixed_digital which rate converts any input. Since it appears that mythtv already does this, it isn't very useful. When I tested it, it also seemed to degrade the audio quality. You probably don't want to use ALSA:mixed_digital or mixed_analog.

You can also use the alsa plugins using this file. I haven't found any plugins useful with mythtv. If you know of a useful one, please update this! In particular, it would be useful to use both analog and digital outputs simultaniously.

--EDIT (Roland): The following additions to .asoundrc work for me to have both digital and analog output work simultaniously:

pcm.!default {
type plug
slave {
pcm multi
rate 48000
}
ttable.0.0 1.0
ttable.1.1 1.0
ttable.0.2 1.0
ttable.1.3 1.0
}

pcm.stereo {
type plug
slave {
pcm multi
rate 48000
}
ttable.0.0 1.0
ttable.1.1 1.0
ttable.0.2 1.0
ttable.1.3 1.0
}

ctl.stereo {
type hw
card 0
}

pcm.multi {
type multi
slaves.a.pcm "analog-hw"
slaves.a.channels 2
slaves.b.pcm "digital-hw"
slaves.b.channels 2
bindings.0.slave a
bindings.0.channel 0
bindings.1.slave a
bindings.1.channel 1
bindings.2.slave b
bindings.2.channel 0
bindings.3.slave b
bindings.3.channel 1
}

ctl.multi {
type hw
card 0
}

• Please note:* Where it says analog-hw and digital-hw ensure you either have these names defined in the asoundrc file or you explicitly define these devices. For example hw:0,2 for Analog and hw:0,0 for digital on a nForce2 audio chipset.

Unfortunately, only stereo will be routed to both analog and digital. I came to the understanding that the nforce2 hardware won't support this approach for 5.1. So when I'm watching a movie with xine (configured to passthrough) that has ac3 output I no longer get the analog output.

-- Roland

Using alsamixer

Some volume settings may be set to 0 or muted (not sure if this is happening anymore on the latest release or not). If you are getting no sound, run alsamixer and make sure the volume controls are set correctly. If you do a normal shutdown, it looks like the settings are save (I haven't been able to confirm). If not do a alsactl store.

Using Digital AC3 Passthrough

Once you get everything working, you might want to try turning this on to see if AC3 will then go straight to your receiver. The down side is that if a non-AC3 track is played, you hear only noise. This should be fixed in Mythytv 0.19 when this option will be disabled for non-AC3 audio tracks.

Using mythtv volume controls

If you want to use the mythtv volume controls, try enabling this. Be aware that this may prevent some digital audio from passing through transparently (ex. no more dolby digital). Also it may reduce audio quality (yet another volume control in the path).

Original Page

Digital Audio and nForce2/nForce4 and MythTV (and SB Live + SPDIF daughterboards)

This is an attempt to list the steps I took to get digital output (a.k.a. optical out or S/PDIF out) working with MythTV and my nForce-based motherboard, a Shuttle SN41G2. I can't say that all these steps are necessary, but they're what worked for me. YMMV.

1. Install KnoppMyth (this is the easy part :) I am using R4V4.1 currently.

--EDIT: This page has been modified to work with R5A10.

--EDIT(alien): I had success in R5A12 by only doing step 11 (/etc/asound.conf) followed by step 13, except that I edited /etc/modprobe.d/alsa-base instead of /etc/modutils/alsa-0.9-knoppix. I could then use /dev/adsp for both LiveTV and MythMusic. Note: During an upgrade, the asound.conf may already be created during the mythrestore.

--EDIT for R5A10, I only needed to follow steps 10 and 13 to get the digital out working on my Abit NF7-S Nforce 2 Motherboard. I set audio for Live TV and music to /dev/adsp0 YMMV.

2. Open an Xterm window and check that your nForce2 motherboard is set up correctly:

cat /proc/asound/pcm

If you see:

00-00: Intel ICH : NVidia nForce2 : playback 1 : capture 1
00-01: Intel ICH - MIC ADC : NVidia nForce2 - MIC ADC : capture 1
00-02: Intel ICH - IEC958 : NVidia nForce2 - IEC958 : playback 1

you are in good shape: skip to step #10!

--EDIT: R5A10 comes with alsa 1.0.6 already installed. Skip to step #10!

--EDIT: If you feel like reading steps #3 to #9 - Ignore the comments in #4 about breaking mplayer (mplayer will still work). I'm not too sure about the comments in #4 about 1.0.6 causing problems with HDTV, but my HDTV channels all appear to be very jerky.

If you only see:

00-00: Intel ICH : NVidia nForce2 : playback 1 : capture 1

you'll (apparently) need to recompile alsa for your nForce2 mobo. At least that's what I did and it worked. Follow these next steps to do so.

3. su to root and go to the /usr/src directory:

su
cd /usr/src

4. Download the latest alsa-driver, alsa-lib, and alsa-utils from http://www.alsa-project.org/ to the /usr/src directory. You'll need to get the same versions from each ftp directory. Note: This will break the mplayer installed with KnoppMyth. If you want to use the current mplayer, stick with alsa 0.9.x, or upgrade your mplayer In the wget commands that follow, substitute the version you're getting with the version I used (which was 1.0.5rc1), and substitute mirror sites if appropriate:

wget ftp://ftp.alsa-project.org/pub/driver/alsa-driver-1.0.5rc1.tar.bz2
wget ftp://ftp.alsa-project.org/pub/lib/alsa-lib-1.0.5rc1.tar.bz2
wget ftp://ftp.alsa-project.org/pub/utils/alsa-utils-1.0.5rc1.tar.bz2

There are messages in myth-dev about alsa 1.0.6 causing video playback problems for HDTV output. Best to stick with 1.0.5rc1 until it is settled out.

5. Now expand the files you just downloaded.

tar -xjf alsa-driver-1.0.5rc1.tar.bz2
tar -xjf alsa-lib-1.0.5rc1.tar.bz2
tar -xjf alsa-utils-1.0.5rc1.tar.bz2

6. To get the source to compile you'll also need to expand some kernel stuff. In my case with R4V4.1 it was:

tar -xjf linux-2.4.25-chw.tar.bz2

7. At this point I pretty much followed the directions for the nforce motherboard found on Alsa's page for nForce2 support Again, substitute your alsa info for what I'm using below:

cd alsa-driver-1.0.5rc1
./configure --with-cards=intel8x0 --with-sequencer=yes
make
make install
cd ..
cd alsa-lib-1.0.5rc1
./configure
make
make install
cd ..
cd alsa-utils-1.0.5rc1
./configure
make
make install

8. Insert the modules into the kernel:

modprobe snd-intel8x0
modprobe snd-pcm-oss
modprobe snd-mixer-oss
modprobe snd-seq-oss

9. Now do a post-install check of your motherboard.

cat /proc/asound/pcm

You should see:

00-00: Intel ICH : NVidia nForce2 : playback 1 : capture 1
00-01: Intel ICH - MIC ADC : NVidia nForce2 - MIC ADC : capture 1
00-02: Intel ICH - IEC958 : NVidia nForce2 - IEC958 : playback 1

10. Check your mixer settings with alsamixer:

alsamixer

WIth the non-GUI alsamixer, use your left and right arrow keys to scroll through all mixer settings, and up and down arrows to increase or decrease levels. Make sure that the IEC958 settings are not muted. If an "M" appears above that channel, press M to unmute it. (Many of these settings are more easily set with the GUI-based gnome-alsamixer... you can always apt-get install it if you would rather use it.)

After making changes via alsamixer (and pressing Esc to exit and save changes), store the settings via:

/usr/sbin/alsactl store

11. Use the asoundrc file found at this excellent Digital Sound HOWTO page (Read it too while you're at it. :) The asoundrc file is found half way down the page and is called "The (I hope it's the definitive) .asoundrc for nForce2". This file can be placed either in ~/.asoundrc or /etc/asound.conf. I placed it in the latter location:

cd /etc/
nano asound.conf

(copy and paste asoundrc file into the document, save changes, exit nano)

NOTE: If you have an nForce4 chipset and are using KnoppMyth R5A15.1, using this asound.conf will _prevent_ you from getting digital audio. For now, just don't use an asound.conf.

--EDIT: I got everything to work on a IEC958 chipset using this asound.conf:

pcm.!default {
type plug
slave {
pcm "spdif"
rate 48000
format S16_LE
}
}

Then changing the audio to ALSA:default and adding alsa:device=default to my mplayer line

-- EDIT: SB Live people can skip this step.

12. Start up MythTV frontend again. Go to Settings->General and change Audio from "/dev/dsp" to "ALSA:Analog" just to test. Start a recording or live TV. You should hear audio via the analog outs as usual. Then return to the general settings and change Audio to "ALSA:Digital" to activate digital output. Return to a recording or live TV. You should hear audio via your digital out. (You may need to use the strings ALSA:analog and ALSA:digital, they seem to be case-sensitive on my system. --liv2cod)

This may have changed with release KnoppMyth R4V5. The setting "/dev/adsp" seems to work now for Settings->General. There may be further developments so stay tuned...

--EDIT: R5A10 is a bit different here. Setting to "/dev/adsp" does not work (might be because step 13 is required first). You need to set it to "ALSA:digital" and also uncheck the "Use internal volume controls" checkbox. You will see that the mixer settings disappear (they're not needed i guess becos of the external alsa mixer??). If "ALSA:digital" does not work, try "ALSA:spdif" instead.

-- EDIT: For people with SB Live + SPDIF daughterboards, you can use "ALSA:iec958" for digital AC3 out. Also check to enable AC3 to SPDIF passthrough.

13. In order to get MythMusic to play through the digital out, do the following additional setup (as root):

--EDIT(alien): In R5, this file is /etc/modprobe.d/alsa-base.

--EDIT also if U using RealTek? ALC655 replace "adsp_map=2" with "adsp_map=4" and use "/dev/adsp" as output

su
nano /etc/modutils/alsa-0.9-knoppix

(or use your text editor of choice). At the bottom of the list, along with other listed options but before the line marked # --- END, add the following line:

options snd-pcm-oss adsp_map=2

Then save changes and exit your text editor. Enter the next two commands (while still root):

update-modules
depmod -a

Then reboot your MythTV box.

shutdown -r now

Once your system has restarted and MythTV's front end has run, go to Setup->General and change your audio device from /dev/dsp to /dev/adsp . Press Enter after making the change to this line... if you cursor down to the Next button and exit the setup menu this way, your change will not be saved and audio device will remain as /dev/dsp.

MythMusic should now play back through your digital out.

14. To get DVD audio playback through your digital audio out, while in MythTV's front end, go to Setup. Add the following to the mplayer command line for both DVD and video playback:

-ao alsa:device=hw#0,2 -ac hwac3,

(NOTE that extra comma at the end of the line. It lets AC3 data passthrough the optical out for hardware decoding, and does software decoding for anything else. The -ao option was what ended up working for me: there's about four bazillion other variations on that out there, but that's what finally did it for me.)

--EDIT: This also works for R5A10.

--EDIT: For SB Live + SPDIF daughterboard, you can use device HW#0,0. (-ao alsa:device=hw#0,0 -ac hwac3, ). If this does not work, try -ao alsa -ac hwac3,

--EDIT: for SB live and new mplayer version (testeed with 1.0pre6-3.3.5) the format is slightly different -ao alsa:device=hw=0.2

--EDIT: R5A12 - for a Shuttle SN41G2V2 and xine

Go edit /home/mythtv/.xine/config

1.) Make sure that audio.speaker_arrangement says Pass Through

2.) Comment out the line starting with audio.alsa_a52_device:iec958....

--EDIT: i had some problems after upgrading to latest xine-lib-1.1.1 and xine-ui 0.99.4 -- this is what worked for me

As before, go edit /home/mythtv/.xine/config

1.) Comment out all lines that have anything to do with audio

2.) Use the following settings:

device.alsa_front_device:plug:spdif:0

audio.output.speaker_arrangement:Pass Through

If you used the steps above to compile the newest version of ALSA, you will probably need to also upgrade mplayer, as the newer 1.x ALSA drivers won't be recognized by the version of mplayer that's included with KnoppMyth R4V4.1. You can either upgrade your version of mplayer via apt-get, or compile a 0.9.x version of ALSA instead.

--EDIT: R5A10 includes a newer version of mplayer that works with the ALSA version.

(Note: when I installed via apt-get, I got a version of mplayer specific for my processor, which also ended up being in a different path than the mplayer that comes with KnoppMyth. I continued not to get audio until I changed the path in MythVideo player setup to the new mplayer, and the -ao option to the one listed above)

To enable AC3 passthrough in xine, use xine's Setup menu, select Audio, and pick Passthrough from the Speaker Arrangement drop-down menu. Although it's not marked as such, you have to restart xine in order for the change to take effect and to hear digital audio.

--EDIT Chaintek AV-710

I am using it only for 2 channel pcm (non-ac3 stuff), passthrough ac3 (dts and dd5.1 and "bit-perfect" wav files for dts music through my hk 5.1 receiver's optical input.

Myth internal and mythmusic work great for this spdif passthrough checked device = /dev/adsp

MythVideo using mplayer command line:

mplayer -fs -zoom -quiet -vo xv %s -ao alsa:device=iec958 -afm hwac3

Xine: Xine: settings for dvd playback

xine -pfhq --auto-scan dvd

Pasted from <http://mysettopbox.tv/phpBB2/viewtopic.php?t=337>;

Xine changes won't stick unless you do this as user mythtv su mythtv nano /home/mythtv/.xine/config

change driver from oss to alsa

1. audio driver to use
2. { auto null alsa oss arts esd none file }, default: 0

audio.driver:alsa

Also, changed part of this but don't know if it was necessary. The comment sign shows as a number rather than a pound sign. sorry. cat /etc/asound.conf pcm.envy_spdifdmix {

pcm.envy_spdif {

1. pcm.!default {
2. type plug
3. slave {
4. pcm envy_spdifdmix
5. }
6. }

1. changed default above for xine to work with knoppmyth R5E50

pcm.!default {

1. For ogle

pcm.!spdif {

1. For mplayer ao (mplayer -ac hwac3 -ao alsa1x:mplayer)
2. For vlc, use mplayer as alsa device

pcm.!iec958 {

pcm.mplayer {