[mythtv-users] Followed Digital Sound setup, many how-to's, and still completely lost.

Rich West Rich.West at wesmo.com
Sat Feb 3 20:24:36 UTC 2007

Rich West wrote:
> Steven Adeff wrote:
>> On 2/3/07, Rich West <Rich.West at wesmo.com> wrote:
>>> Rich West wrote:
>>>> *sigh*  I am reluctantly sending this to the listt, but no matter what I
>>>> try, I cannot seem to get consistent results from any of the "digital
>>>> sound" how-to's.
>>>> Goal:
>>>> Pump all sound out via SPDIF and let my receiver do the work.
>>>> Near Goal:
>>>> Hey, I would be content if I just had to switch the input on my receiver
>>>> from the TV setting (L/R stereo in)) to my DVD setting (Optical 5.1
>>>> Audio in).
>>>> What I have tried so far:
>>>> http://www.mythtv.org/wiki/index.php/Configuring_Digital_Sound#ALSA_Utilities,
>>>> http://gentoo-wiki.com/HOWTO_Dolby_Digital_Out_(AC3,_SPDIF) (I have FC5,
>>>> but I thought some of it might apply), along with following a couple of
>>>> threads in the list.
>>>> Here's where I am at:
>>>> <..snip..>
>>>> Although I've read the Wiki's, How-To's, and other postings, I just feel
>>>> like I am missing something simple here...
>>> Muhaha.. I just got things working.  I missed the thread from "Josh
>>> <TwoOneSix at thatclothingco.com>" titled "Re: [mythtv-users] M-Audio
>>> Revolution 5.1 and FC6 [Working!]".
>>> The piece I was missing was (sort-of) listed in his message.  I needed
>>> to set the default audio-output to ALSA:default along with the
>>> passthrough device to ALSA:default.
>>> Watching LiveTV and watching recordings now outputs via the SPDIF
>>> optical connection (interestingly, my receiver flips to "Dolby
>>> Prologic"), and watching DVD Video's also outputs the sound via SPDIF
>>> optical and the receiver properly sees the incoming stream as AC3.
>>> Interestingly, though, MythMusic no longer outputs anything.. Gotta look
>>> in to that.
>>> BYW: Thanks Josh!
>>> -Rich
>> MythMusic has a separate device option, so you just need to go into
>> the MythMusic settings and change it to match what you have for TV.
> After seeing in my mythtvfrontend.log (I never even knew that there was 
> a "-v audio" option to mythfrontend. :) ):
> 2007-02-03 13:42:04.346 Opening ALSA audio device 'spdif'.
> 2007-02-03 13:42:04.347 in SetParameters(format=2, channels=2, 
> rate=44100, buffer_time=500000, period_time=125000)
> 2007-02-03 13:42:04.348 AudioOutput Error: Rate doesn't match (requested 
> 44100Hz, got 48000Hz)
> And then seeing your message, I changed the output device to /dev/dsp.  
> Muhahah.. that worked.  I just set it to /dev/dsp to use the L/R audio out.
> It's actually kind of interesting that the optical input on my receiver 
> is tagged as "CD Optical Audio In".  CD's are 44.1khz, right?
> Too bad I can't pump everything through the optical connection.. I 
> wonder why it won't send it at 44.1khz..

Wow.. didn't realize just how close I was. :)

I updated /etc/modprobe.conf to include:
options snd-pcm-oss adsp_map=1

As per the KnoppMyth Wiki (I'm not running KnoppMyth, though), but that 
alone did not help.  However, a little further UP in that wiki entry, I 
came across an /etc/asound.conf entry:
pcm.!default {
type plug
slave {
pcm "spdif"
rate 48000
format S16_LE

I put that in place, updated the default output device and passthrough 
device to be "ALSA:default" and set the MythMusic device back to "default".

Viola!  Everything goes through the optical connection... :)


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