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Trouble with 5.1 out over S/PDIF

post #1 of 12
9/30/07 at 9:57pm
Thread Starter 
Hi all,

I'm having some trouble getting the sound on my MythTV working.

I've got an onboard Intel 82801G (ICH7 Family) HD sound card with a homemade S/PDIF coax cable hooked to the motherboard. I have no trouble with 2 channel sound, but when I enable AC3/DTS passthrough in MythTV, I get no audio.

It actually does play sound for about 50ms (give or take...but the units are correct there, i.e., 1/20 of a second...just a blip). This blip of sound does actually appear to be from the content playing (it's not noise). But after that its dead silent. The receiver is recognizing the input as 5.1 or 2 channel, depending on the content, i.e., the Display lights up "Dolby Digital [3/2]" or "Dolby Digital [2/0]" appropriately.

In order to actually hear sound, I have to disable AC3 passthrough and listen to it in 2 channel.

Thanks much for any help!
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post #2 of 12
10/1/07 at 10:32am
What is your sound card? Digital surround sound in mythtv gave me problems to no end. I was using SB Live! w/ALSA drivers however I switched to Vista awhile ago but if I remember correctly here is what I did:

1. Endlessly fiddled with the MythTV "Audio output device". The text that goes there was case sensitive and took lots time and lots of forum reading to figure out. I had to learn to use ALSA command line tools like "aplay -l" and speaker test tools to find the proper output device on my card. DD/5.1 surround was PIA and the biggest hurddle for me when using Mythtv.

2. Uninstalled/re-installed all versions of ALSA drivers until I found one that worked.
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post #3 of 12
10/6/07 at 9:41pm
Endoverend -

This is an annoying issue with output levels and muting of the ALSA output. I've been running myth since version .7 and i've always had trouble, regardless or disto, getting this right. The problem is is completely non-intuitive to get it setup right. The solution i've found to work over the years follows.

Try this:

Start playback of a surround source on your mythfrontend. Then run,

$ alsamixer

Scroll across until you come upon

'IEC958 Playback AC97-SPSA'

The 'AC97-SPSA' may vary from mobo to mobo ... just find whatever 'IEC958 Playback ' control that pertains to your hardware.

Turn the 'IEC958 Playback ' volume all the way down (down arrow).

Next, find just the 'IEC958' item (usually one to the left). There's a good chance this is muted when it shouldn't be. Press 'm' to unmute it.

Vala! You should have sound!

Hope this helps.

Delgas
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post #4 of 12
10/7/07 at 8:55pm
what brand/model of receiver is it. Also it sounds like you may need to change your passthrough devices in Utilities/Setup->Setup->General page 3
I like alsa:spdif or alsa:iec958 as the passthrough device.
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post #5 of 12
10/7/07 at 10:00pm
Thread Starter 
Thanks for the help, but I only have one IEC958 bar in alsamixer and its stuck at 00. Pressing up or down does not work. Where most of the bars are a long vertical rectangle with a square at the bottom, this one is ONLY the square at the bottom. All the other bars are at 100. Muting/unmuting does not change this other than to replace the "00" in the box with "MM".


Receiver is a Sony STR-DE835. It's about 8 years old, was Sony's second from top-of-the-line consumer receiver, typical $400 Best Buy item. Coax in works from another DVD player.

Have played with the page3 stuff, that was the only way to get to the receiver to sense a 5.1 signal.

It is DEFINITELY playing 5.1 audio out for the 1/20 of a second as mentioned. So its getting there, its just immediately cutting out.

Thanks again for all looking at this. My next course of action is to redo this box in 11 days when Ubuntu 7.10 goes final.
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post #6 of 12
10/8/07 at 5:29am
You sure the receiver isn't the issue. Perhaps the 8 year old receiver isn't handling the output correctly
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post #7 of 12
10/8/07 at 12:28pm
I have a somewhat unique issue with SPDIF sound output as well that appears to be some sort of syncing issue. I have an M-Audio Revo 7.1 soundcard and I have to yank the SPDIF cable from my receiver and plug it in after the kernel starts initializing. If I put it in earlier or later, I don't get any sound. I'm not sure if its on point, but you might try some of the same black magic.
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post #8 of 12
10/8/07 at 1:41pm
This may be completely unrelated, but on the frontend I use onboard spdif on I have had problems sometimes with the sound just randomly stopping after boot or after restarting X. It used to puzzle me but I found killing the esd daemon always fixed the problem for me (before then I used to reboot). It seemed esd was conflicting or something.

Do you get any audio messages from mythfrontend when this happens? Have you tried playing a file back with mplayer or similar using ac3 passthrough? That could help isolate whether it is a myth or larger problem. For me it was a larger problem, especially since I have my .asoundrc put all sounds through spdif by default.

Also does this happen everytime you play anything from myth (recordings, mythvideo, dolby digital files) or does it only play a little bit for the first file you open and then subsequent files you get no sound?
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post #9 of 12
10/8/07 at 3:56pm
Thread Starter 
Quote:
Originally Posted by blackoper View Post

You sure the receiver isn't the issue. Perhaps the 8 year old receiver isn't handling the output correctly

My old DVD player works fine with the Coax-S/PDIF. I tested it after I started having this problem, so I think the receiver is behaving.

Quote:
Originally Posted by drkdiggler View Post

I have a somewhat unique issue with SPDIF sound output as well that appears to be some sort of syncing issue. I have an M-Audio Revo 7.1 soundcard and I have to yank the SPDIF cable from my receiver and plug it in after the kernel starts initializing. If I put it in earlier or later, I don't get any sound. I'm not sure if its on point, but you might try some of the same black magic.

Quote:
Originally Posted by newlinux View Post

This may be completely unrelated, but on the frontend I use onboard spdif on I have had problems sometimes with the sound just randomly stopping after boot or after restarting X. It used to puzzle me but I found killing the esd daemon always fixed the problem for me (before then I used to reboot). It seemed esd was conflicting or something.

Do you get any audio messages from mythfrontend when this happens? Have you tried playing a file back with mplayer or similar using ac3 passthrough? That could help isolate whether it is a myth or larger problem. For me it was a larger problem, especially since I have my .asoundrc put all sounds through spdif by default.

Also does this happen everytime you play anything from myth (recordings, mythvideo, dolby digital files) or does it only play a little bit for the first file you open and then subsequent files you get no sound?

Played around with the cable a bit, turning receiver on/off connecting/reconnecting cable...no dice. Same behavior...correctly sets 5.1 audio (the receiver's big blue "ooo it's digital! light" turns on)... plays a 1/20 blip of sound. Also tried killing ESD (was running, but didn't change anything). mplayer has the same behavior. Same behavior on DVD, recorded HDTV, and ripped DVD. Still need to run mythfrontend from a console and check for messages...but IIRC, there were not any audio specific messages last time I tried that.

My guess at this point is that something's buggy in the kernel or alsa driver. Fingers crossed that it just fixes itself in 7.10.

And again, thanks for all the suggestions everyone, REALLY appreciate the help!
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post #10 of 12
10/8/07 at 4:04pm
Quote:
Originally Posted by endoverend View Post

My old DVD player works fine with the Coax-S/PDIF. I tested it after I started having this problem, so I think the receiver is behaving.





Played around with the cable a bit, turning receiver on/off connecting/reconnecting cable...no dice. Same behavior...correctly sets 5.1 audio (the receiver's big blue "ooo it's digital! light" turns on)... plays a 1/20 blip of sound. Also tried killing ESD (was running, but didn't change anything). mplayer has the same behavior. Same behavior on DVD, recorded HDTV, and ripped DVD. Still need to run mythfrontend from a console and check for messages...but IIRC, there were not any audio specific messages last time I tried that.

My guess at this point is that something's buggy in the kernel or alsa driver. Fingers crossed that it just fixes itself in 7.10.

And again, thanks for all the suggestions everyone, REALLY appreciate the help!

Good luck. I'm out of ideas...
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post #11 of 12
10/10/07 at 2:40pm
Well I don't use Myth I use Freevo, but I might be able to help at least figure out if your system can play 5.1 using mplayer. But first in need to see the output from a shell prompt when you run "aplay -L" before I can provide the command for mplayer?
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post #12 of 12
11/4/07 at 1:46am
Thread Starter 
Just wanted to follow up on this thread...

I just installed mythbuntu 7.10. The 5.1 problem is solved, DVDs and HDTV both provide 5.1 surround now.

Thanks again for all the suggestions everyone, really appreciate it even though it looks like it turned out to be that the 7.04 driver just wasn't compatible with my hardware.
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