[mythtv-users] scratchy sound troubleshooting

[gibman]

Kevin,

I'm having the SAME problems.. argh.  However if I turn my volume up a
little higher, I do hear the audio, it's just garbled and distorted,
lots of noise.  Here are a few things I tried that DIDN'T help me, but
hey, they might help you?  Who knows...  (as well as a few things I
plan to try)

1- For kicks, try using the MIC port instead of line in (if you have a
patch cable).  I went into alsamixer and bumped up the MIC, hit F4
went to line in and removed CAPTUR (space) and then arrowed over to
MIC and made it CAPTUR.  Started tvtime, aplay /dev/dsp, same deal,
really horrible sound.
-- why I bring this up: It's just troubleshooting.  I switched things
back to the line-in.  And BTW, using tvtime and the FC ALSA gui, the
sound is _perfect_.  (/dev/dsp is still hosed)

2- Gain Control
I was reading this last night:
http://www.gossamer-threads.com/lists/mythtv/users/75579?search_string=sound;#75579

However using alsamixer and aumix I don't see a gain control anywhere
(Alsamixer it's?.. and "IGain" in aumix apparently ).  I'm partially
convinced it is a gain problem as while I mess with all the other
controls, it's just different volume levels of distorted sound.

3- Sample Rate 
>From the above URL:
"Unfortunately, I have not yet found a solution, aside from setting
the playback sampling to 48KHz (which can be done for mplayer and
mpg123, but I have not found a way to
have mythtv do this)."

Robert's Guide makes mention of setting some of these via the command line:
http://cvs.mythtv.org/cgi-bin/viewcvs.cgi/mythtv/docs/mythtv-HOWTO.txt?rev=1.232
Which did me no good, but I tried anyway ( as well as reducing the
levels as suggested).

Argh!... Googling around right now I found this:
http://www.linux.com/howtos/Alsa-sound-7.shtml (half way down)
--
Gain

Most sound cards have a separate mixer part for extra input or output
boosting. This entry is most likely called the ``gain'', ``in-gain''
for input and ``out-gain'' for output. Setting this gain to an
appropriate level will greatly help you getting the maximum volume out
of your speakers...

amixer set out-gain 100 unmute

I'll try this later on, but the control doesn't show up in aumix or
alsamixer, so I'm not sure if the command line version will work?
humph.

I can't watch Live TV, I don't know why it just makes the screen go
blank so I don't know if I get distorted sound in live TV, I can only
assume I do (as I do in recorded programs).  It's either the gain or
the sample rate. (I think)

 If the above doesn't work, you can try setting custom sample rates in
an .asoundrc .  I get that notion from:

http://www.alsa-project.org/alsa-doc/doc-php/asoundrc.php?module=Generic
--
	pcm_slave.sl2 {
     		pcm
     		rate 48000
	}

	pcm.rate_convert {
     		type rate
     		slave sl2
	}

Now you can call this newly created virtual device by:

	aplay -D rate_convert test.wav

I don't know if myth supports alsa alias, but we could theoretically
change /dev/dsp in myth to "rate_convert".  (Haven't tested, don't
know, it's just a guess)  Sorry for the rant, it's been a rough few
weeks.

Please let me know if you solve this first!
J

(PS: I'm 0.16 / FC 2 / Cheapie PCI sound card)

On Tue, 11 Jan 2005 20:50:50 -0800, Kevin Brouelette <kevin1a at varlog.net> wrote:
> 
> 
> Hi
> 
> I have mythtv 0.16 running on Fedora3/Alsa with my onboard sound card
> SiS SI7012.  I had no sound problems watching or recording TV.
> I changed out the Win-TV [bttv w/ FM radio and IR] to a Win-TV-Go card.
> Since mythv only needs to connect to my cable TV, I use the better card
> in another system for my camera server [zoneminder.com] and the cheaper
> 'Go' capture card for Mythtv.  [The 'Go' was < $19 incl shipping on
> ebay].
> 
> Now my 'watch tv' sound is really scratchy.
> xawtv and 'tvtime' are fine so I think the card is ok.
> Recorded shows are also scratchy.
> I did the troubleshooting suggested in the documentation:
> a] run xawtv and mute the sound
> b] run 'aplay /dev/dsp'
> 
> I don't here the delayed tv sound but I do hear raw scratchy noise.
> So, the scratchy is coming from /dev/dsp [??]
> I've been changing settings in alsamixer but I haven't resolved
> the problem yet.
> 
> Any help is most grateful,
> TIA
> 
> Kevin B
> 
> 
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