[mythtv-users] Shuttle SK41G sound problem

[Steven Marcotte]

On Fri, 2003-12-19 at 22:07, Joseph A. Caputo wrote:

> You really should be able to use the same volume levels as mplayer.  When you 
> play something with mplayer, does it output to /dev/dsp or /dev/adsp?  Try 
> configuring Myth to output to /dev/dsp if that's the default.

mplayer is using /dev/dsp as output.

> Finally, if you can try testing with XawTV in the following manner:  bring up 
> xawtv and a mixer.  Watch TV with xawtv.  While watching, set your Master & 
> PCM to comfortable levels.  Now, in an xterm, enter the command 'aplay 
> /dev/dsp' and leave it running.  You *should* hear doubled audio... one audio 
> stream with the video and one a tad behind.  It may not be overly noticeable.  
> Now, while that's going on, mute the 'CD' mixer slider.  You should get a 
> single audio stream which may be a little behind the video.  If you don't, 
> you need to make sure that the 'CD' input is set as the capture source, and 
> that the capture volume is turned up to an appropriate level.  On some 
> mixers, 'mute' is a simple toggle, and the capture level is simply the level 
> of the selected capture source (here, 'CD').  On other mixers, 'mute' sets 
> the level of the selected source to zero, and there is a separate slider for 
> the capture level.

OK, if I open xawtv and enter the command 'aplay /dev/dsp' and adjust
the levels in aumix as follows:

Volume: 70
PCM: 70
CD: 100
IGain: 100

The volume level is fine, there is no distortion, and there are two
audio tracks.  If I set the CD input to 0, one audio track goes away and
I am left with on audio track slightly out of sync.

If I quit aplay, aumix, and xawtv and start MythTV with the same levels,
I get the same result, loud and distorted.  I can adjust the audio
levels down, and the volume will get lower, but the distortion remains. 
In fact if I set the levels in aumix as follows, the sound is very quiet
but still distorted.

Volume: 20
PCM: 20
CD: 0
IGain: 2

I can play music from Myth Music with the same levels as the xawtv
experiment, and it plays fine.  

ALSA registers two DSP devices for my via82xx sound card, /dev/dsp and
/dev/adsp.  I reran the xawtv experiment with for /dev/adsp, with the
following levels:

Volume: 70
PCM: 70
CD: 100
IGain: 100

The output is loud and distorted, there is too much distortion to tell
if there is two audio tracks.  If I set the IGain level to 0 the
distortion goes away and you get a normal sound output in real-time from
the CD channel.  

I thought this is great, finally I'm able to reproduce the problem
outside of MythTV.  The first thing I did was double check to make sure
that neither the Myth front-end or back-end was configured to use
/dev/adsp.  But as luck would have it, MythTV was configured to use
/dev/dsp for capture and playback; lsof verified that this was the case.

The via82xx chipset is suppose to support full-duplex mode.  I have run
the gamut of related module parameters with no success.  But shouldn't a
TV recording be fine regardless of weather or not my soundcard supports
full-duplex?  lsof reports that the only process accessing /dev/dsp is
the MythTV back-end, and that is in read-only mode.

The only thing I can conclude is that my TV card is a piece of junk, so
it looks like no MythTV for me.  Thanks for all your help.

Quattro