Problem enabling sp/dif on Gigabyte K8VM800M / Realtek ALC655 on-board audio

[Mark Linford]

Mark Linford wrote:

>Hello, everyone:
>
>I'm trying to enable sp/dif (digital) output with my new Fedora Core 4 (x64) 
>install, and I'm having a heck of a time trying to get it to work. Here's my 
>basic setup:
>
>* Gigabyte K8VM800M motherboard
>* Realtek ALC655 on-board audio
>* Logitech Z-5500 surround speakers
>
>I'm able to get sound via the analog outputs without problems, but nothing 
>comes from the digital output. As this is the first setup with digital 
>outputs I've ever tried, I'm at somewhat of a loss were I should even begin.
>
>One interesting thing I did notice. My speakers have an lcd control panel 
>which can show if it's detecting a digital signal or not. Normally, this 
>shows "No Input Detected" when using the optical (digital) input on the 
>speakers. However, after playing around in alsamixer, I noticed that if I 
>changed the setting for IEC958 from "IEC958 In" to "Analog In", my speakers 
>detect a signal, though there's no audio coming out. IEC958 Output is set to 
>"00" (with no way to change it. IEC958 Playback AC97-SPSA is set to 
>"100" (also, when I move this slider up and down, I hear an audible "pop" 
>through the speakers). External Amplifier is set to "off," and I can't seem 
>to change that setting either.
>
>So, I'm stumped. Any advice on how to proceed would be appreciated.
>
>Mark
>
>  
>
Well, I got it fixed. After a little more google'n, I found some helpful 
info from the MythTV/Fedora HOWTO page:

http://wilsonet.com/mythtv/fcmyth.php#alsa

Specifically, I found this blurb:

"While enabling S/PDIF out for my Audigy was a matter of a checking a 
box in gnome-alsamixer, some folks have reported having to set a 
particular slider (IEC958 something-or-other?) to zero to enable the 
S/PDIF output on their sound cards. Go figure."

So, looking at all of the sliders in alsamixer, set IEC958 Playback 
AC97-SPSA to "0," and also set IEC958 to  "PCM." Voila!  Now, my sound's 
coming out of the optical port. I don't pretend to know what I did, but 
at least it works :)