[mythtv-users] Shuttle SK41G sound problem

[Joseph A. Caputo]

On Friday 19 December 2003 15:31, Steven Marcotte wrote:
> On Thu, 2003-12-18 at 12:15, Joseph A. Caputo wrote:
> > On Thursday 18 December 2003 11:59, Steven Marcotte wrote:
> > > ARRRGHHHH!  I need help.
> > >
> > > I'm setting up a new Myth box and I have a problem with the sound. 
> > > The TV card is a generic BT8x8 card without a DSP, so the internal
> > > audio out on the TV card to the CD in on the motherboard.  The
> > > hardware seems to works fine; I can use aplay to play sounds through
> > > the ALSA driver, I can use xawtv to watch TV with sound.  I can not,
> > > however, start xawtv, mute the CD in, and successfully execute 'aplay
> > > /dev/dsp'.
> > 
> > This may be for one of 3 reasons:
> > - You need to set the CD as the capture input in your mixer
> > - CD is the capture device, but 'muting' it sets the volume to 0.  Look 
> > for a separate slider for the 'Capture' volume.
> > - Your card/driver doesn't support full duplex (ie, simultaneous record/
> > playback
> > 
> > For the first 2 issues, see below.  For the third, you either need new 
> > drivers, a new sound card, or both.
> > 
> > >
> > > This is where it gets weird.  If I start watching Live TV, and I set
> > > the volume to 50%, the CD to only 5%, and unmute the CD in, it is
> > > distorted and LOUD, VERY VERY LOUD!  I'm talking blood from the ears
> > > loud!  The audio that is played is the raw audio feed, it is not in
> > > sync with the video.
> > >
> > > xawtv doesn't have this problem, I can set the volume to 50% and the
> > > CD to 100% and it is a nice respectable listening level; in fact, it
> > > is almost too quite.
> > >
> > > I originally tried Gentoo with a few different kernels and the ALSA
> > > 0.98 drivers, with no luck.  I thought maybe the problem was my
> > > aggressive CFLAGS so I installed KnopMyth R4.  Still no luck.
> > >
> > > Anyone have any suggestions?
> > >
> > > HARDWARE
> > > Shuttle SK41G
> > > AthlonXP 2400+
> > > 512MB PC2700
> > > Maxtor 120 GB HDD
> > > Generic BT8x8 based card
> > >
> > > SOFTWARE
> > > KnopMyth R4
> > > via82xx ALSA driver
> > > bttv video driver
> > 
> > 
> > Okay, here's what MIGHT be going on:
> > 
> > When using Xawtv, 3 mixer controls affect the overall volume:  'CD' and 
> > 'Master Volume', plus the output volume of your tuner card (technically 
> > not a mixer slider, but you get the idea).  When *recording* with 
> > MythTV, the controls 'CD' (possibly plus a separate 'Capture' slider, 
> > depending on your sound card/driver/mixer app) and the output volume of 
> > your tuner card affect the volume of the encoded file.  When *playing 
> > back* with Myth (either playing back a recorded program or LiveTV), 
> > there is a change:  the 'CD' (and 'Capture') controls do not affect the 
> > output volume of the playback, but 'Master Volume' and 'PCM' do.
> > 
> > To properly adjust your volume, you should adjust the playback and 
> > recording volumes separately.  To adjust your playback volume, use 
> > something like mplayer + a DVD or ripped movie (a known good file), and 
> > adjust the 'PCM' and 'Master Volume' while it's playing.  Make a note 
> > of the settings.  Mine are 'Master Volume' 100% and 'PCM' 75% for good 
> > volume without distortion.  Keep in mind that mythfrontend may try to 
> > reset these volumes on startup; this can be adjusted in 
> > Setup->TV->Playback.  You can have mythfrontend adjust your levels to 
> > these values whenever it starts up, or you can have it leave them 
> > alone.  Your choice.
> > 
> > Now that you've got your playback levels set, you'll need to adjust your 
> > recording levels.  Here you just need to play with the output volume of 
> > your tuner card + the 'CD' slider (on some setups, the 'CD' slider 
> > volume will be '0%' for mute, and there is a separate slider to control 
> > the capture volume).
> > 
> > To summarize:
> > (note: for most people, replace 'CD' with 'Line In')
> > 
> > XawTV:
> > 	Tuner LineOut -> CD Volume -> Master Volume -> sound you hear
> > 
> > MythTV:
> > 	Recording:
> > 	Tuner LineOut -> CD (or Capture) Volume -> encoded file/ringbuffer
> > 
> > 	Playback:
> > 	decoded file/ringbuffer -> PCM Vol -> Master Vol -> sound you hear
> > 
> > LiveTV = Recording -> Playback
> 
> I took your advice and played with the sound levels for different
> programs and this is what I came up with.
> 
> For mplayer, setting the volume and PCM to 60% results in a nice quiet
> level, no distortion.  I can push it up to 100% and although it is very
> very loud, it is not really distorted at all.

Right.  I've found that while I can push 'Master' to 100%, setting PCM above 
about 75-80% gives me distortion, but YMMV.

> With xawtv, setting the volume and CD IN to 75% results in a nice level
> with no distortion.  PCM has no effect, and can be set to 0%.  If I
> crank the CD IN to 100%, you can hear a very slight high pitch tone in
> the background.  I'm attributing that to radio interference from the
> processor.

You don't want to set PCM to 0, because any other apps that play sound will 
then be muted.

> Here is the sound setup for MythTV.  The backend is configured to
> capture audio from /dev/dsp @ 32000Hz.  (/dev/dsp is owned by the
> via82xx ALSA driver)  The frontend is configured as:

Just for kicks, try capturing at a different sample rate.  Some sound cards 
don't like 32kHz.  Do a test with 44.1kHz or 48kHz.

> Output device: /dev/adsp
> Mixer device: /dev/mixer
> Mixer Controls: PCM
> Master volume: 25
> PCM Mixer volume: 25
> 
> When the system boots, the sound levels are set with aumix as follows:
> 
> aumix -v 70 -c 0 -c R -w 70 -m 0
> 
> This configuration with MythTV just blows you away; it is loud and
> distorted.  If I open aumix and set the volume and PCM levels to 3%, the
> sound level is barely audible, but still distorted.
> 
> It's hard to judge, but it seems like watching live TV is more distorted
> than watching a recording of the same show.  Transcoding a recording and
> playing it on another computer plays loud and distorted as well.
> 
> Are there any other audio settings that I have over looked?
> 
> Quattro

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.

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.

In any event, playing with the mixer in this way (running xawtv & 'aplay 
/dev/dsp' simultaneously) is one of the best ways to get the right mixer 
settings.

Good luck,

JAC