[mythtv-users] Digital audio: centre channel drops out intermittently
Marc Sherman
msherman at projectile.ca
Sat Jan 14 14:40:45 UTC 2012
I'm running 0.24-fixes on ubuntu 11.10, and the audio is connected from
my combined fe/be machine to a JVC mini-system amp via spdif. When I'm
watching recorded HD programming (OTA), I frequently but intermittently
get dropouts on the centre channel (which is really bad, because that's
usually where the dialog is).
If I switch mythtv to 2 channel output in setup (still over the spdif
out), there's no dropouts. Similarly, if the prefs are left at 5.1 out,
but I switch the audio channel on a recorded program to an available
secondary 2 channel track, no dropouts. Upmixing is disabled in my
mythtv prefs, but the minisystem has it's own 2->4 upmixing which is
turned on.
I've tried running the speaker test built into the mini system, and
can't reproduce the problem there.
I've tried running "speaker-test -c 6" (which is part of the alsa tools
distro, I think), but it only outputs sound to the front 2 channels, it
goes silent when it's supposed to be testing the other 4 surround
channels. I think that's because it's not encoding the output as AC3?
I'm not sure.
Does anyone have any ideas for how to further isolate the source of this
problem so I can troubleshoot and/or replace the broken component? I'm
still not sure if this is a software problem in mythtv (but then why
only the centre channel?), a soundcard or alsa driver problem (same
question?), or a hardware failure in my minisystem amp (but then why
does the internal speaker test not show the problem?).
The only part of the system I'm convinced is ok is the physical speaker
and the cable running to it (which was actually my first guess, because
we've had a problem with mice :)
Thanks very much for any debugging/troubleshooting pointers...
- Marc
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