[mythtv-users] Shuttle SK41G sound problem

Joseph A. Caputo jcaputo1 at comcast.net
Sun Dec 21 08:42:33 EST 2003


On Sunday 21 December 2003 04:35, Steven Marcotte wrote:
> 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.

What do you mean 'the same levels'?  Depending on your settings, mythfrontend 
may adjust your audio output levels on startup.

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

PCM & IGain are most likely to affect distortion.

> 
> 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.

Is this while watching LiveTV?  If so, mythfrontend should also have /dev/dsp 
open; if it doesn't, then are you sure* that mythfrontend is configured to 
use /dev/dsp for TV playback?  There are 2 places in the frontend setup where 
this is configured -- 1 for mythmusic & one for TV playback.  When changing 
settings you must continue through all the screens until the end, or the 
changes do not get applied.  Based on your observations above, it sure sounds 
like mythfrontend is playing through /dev/adsp.

Beyond that, I don't see anything else you've missed.

Good luck,

JAC



More information about the mythtv-users mailing list