[mythtv-users] ALSA: Cannot mute Capture

[Bruce Markey]

Randy.Tidd at charter.net wrote:
> HI,
> 
> I hope you can help.  I'm trying to setup the mixer as described in the
> documentation:
> 
> http://www.mythtv.org/docs/mythtv-HOWTO-7.html#ss7.2
> 
> $ amixer set Master,0 100%,100% unmute
> $ amixer set Line,0 75%,75% mute captur
> $ amixer set Capture,0 100%,100% mute captur
> $ su
> # alsactl store
> # exit
> $
> 
> I'm having trouble with the 3rd command.  amixer set Capture,0 100%,100%
> mute captur
> 
> Capture will not mute.  It does not seem to have this property.  Before
> running this command:

"Capture" should not be allowed to mute and even if it was, it
should be unmuted. I've always wondered about this. This has been
there for a long time but it appears to be inert.

> I believe this is the cause of the two streams of audio I hear when watching
> live tv.  I hear both the "live" audio and the delayed audio that is in sync
> with the delayed video Myth generates.

Check what happens when you press Pause. The realtime analog
passthrough may continue while the playback of the recorded
date would stop.

>   If I disable "capture" from the
> Capture control, suddenly both audio streams are lost.

That's clearly not what should happen...

>   If I then unmute the
> CD control(the TV tuner is connected to the CD input of the soundcard) I
> then hear the "live" audio which is out of sync with the delayed video as
> expected.  

This is what should happen. For yucks, can you try connecting it
to AUX rather than CD? Or use the external patch cord to connect
to Line? Possibly there is a card/driver quirk with the CD input.

> Similarly xawtv has the same problem.  Despite the CD control being muted, I
> hear live audio.  If I disable "capture" on the Capture control, this live
> audio stops.  If I then unmute the CD control, I can again hear live audio
> as I would expect.

Again, not the correct behavior.

> I realize this is more of an alsa problem, but hoping someone has run into
> the same thing here and can help me out.  This is a gentoo system running
> the 2.6.9-r1 kernel with a Soundblaster Live! using the emu10k1 alsa driver.

Never heard of it. Agreed that this is an alsa problem so you
should probaly do some digging at their site and Google. FWIW
I have an "Creative Labs SB Live! 5.1 Model SB0100" and have used
emu10k1 for every version of alsa 1.0.x and never saw this problem.

--  bjm

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RCS file: /var/lib/mythcvs/mythtv/docs/mythtv-HOWTO.sgml,v
retrieving revision 1.246
diff -u -r1.246 mythtv-HOWTO.sgml
--- docs/mythtv-HOWTO.sgml	19 Oct 2004 06:37:28 -0000	1.246
+++ docs/mythtv-HOWTO.sgml	3 Nov 2004 19:50:16 -0000
@@ -1867,7 +1867,7 @@
 <tscreen><verb>
 $ amixer set Master,0 100%,100% unmute
 $ amixer set Line,0 75%,75% mute captur
-$ amixer set Capture,0 100%,100% mute captur
+$ amixer set Capture,0 100%,100% captur
 $ su
 # alsactl store
 # exit