[mythtv-users] Digital optical surround audio works, but sends "digital noise" to analog audio output

Albert James albertinnyc at yahoo.co.uk
Thu Jan 10 20:11:58 UTC 2008

Hello, first time posting here, thanks in advance for any guidance and thanks to the community at large for such a great technology.

After about 12 months of tweaking, most things on my FC6 Myth are working well, just having a minor audio issue.  The post from Ma made me want to ask this question.  My setup is fairly simple, a 2TB storage server & backend in the basement, a slim HTPC in the media room.

A) I'm using a Asus M2NPV-VM
B) I have the optical digital audio (SP/DIF) daughterboard and can output audio via digital optical just fine (though I have to unmute it manually each reboot in alsamixer..argh!)
C) Digital audio (both stereo and surround/5.1) coming from said optical digital audio output (SP/DIF) work fine.  Receiver shows proper signal type (i.e. stereo, 5.1, etc.)  This is true for playing MythDVD, MythMusic, and I think all possible Myth audio outputs.
D) Analog audio (stereo only) coming from the motherboard's analog audio, as well as the digital optical output, works fine.  This is true for MythMusic, or I think any other stereo source.

When playing a DVD (or any surround/5.1 source), the analog audio output sends nothing but noise (crackles).  This is not a huge problem because my receiver normally auto-detects the digital optical input and uses that instead of analog.  It is a problem for me though, because I use the analog spliced to a multi-zone audio system, and so other rooms get a horrible noise when I play DVD's.

What I was expecting, is the surround (5.1) signal sent to the digital output, and either a downmixed (ideal) signal sent to the analog connector, or only the front left/right signal sent to the analog output.

Can anybody point me in the right direction?  I'm not sure yet if it's a myth issue or a hardware issue.  I'm using ALSA and have enabled AC3/digital output in the myth config screens.

Thanks in advance!!

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