[pulseaudio-discuss] why is this giving an error and failing to start?

Christ Schlacta lists at aarcane.org
Fri Dec 24 17:04:03 PST 2010

...A few days later, Things happened, people showed up..  we turned on 
some more varied christmas music, and immediately there was clipping at 
the high end.  I explained the circumstances, and someone had gotten us 
a new pair of speakers for christmas, we got to hook them up early, and 
this, combined with disabling my method of mono downmixing fixed ALL the 
problems.  no more clipping, all the chipmunks, and the sound is quite a 
bit clearer now than it was with our old speakers before they went.  All 
in all it's a christmas miracle!!

But I'd like to report that this method of downmixing to mono, sadly, 
can result in audio clipping and artifacting.  I've got some idea why, 
and I understand about as well as is beneficial, but at the end of the 
day, I've got no clue how to fix it.  If anyone needs to use this method 
in the future, just know about this issue!

On 12/22/2010 01:41, Colin Guthrie wrote:
> 'Twas brillig, and Christ Schlacta at 21/12/10 19:29 did gyre and gimble:
>> load-module module-combine sink_name=mpd.002 slaves=mpd.001 channels=2
>> load-module module-remap-sink sink_name=mpd.003.lr master=mpd.002
>> channels=2 master_channel_map=left,right channel_map=left,right
>> load-module module-remap-sink sink_name=mpd.003.rl master=mpd.002
>> channels=2 master_channel_map=right,left channel_map=left_right
>> load-module module-combine sink_name=mpd slaves=mpd.003-rl,mpd.003.lr
>> channels=2
>> update-sink-proplist raw device.description="actual soundcard"
>> update-sink-proplist xbmc device.description="XBMC stereo output"
>> update-sink-proplist mpd device.description="MPD Stereo output"
>> ### ENd config snippet.
>> The problem is that I'm getting some perculiar errors on starting
>> pulseaudio:
>> Dec 21 11:19:06 rebirth pulseaudio[14764]: module-combine.c: No slave
>> sinks specified.
> Hmm, interesting. Any idea which of the two combines this message is
> coming from?
>> Dec 21 11:19:06 rebirth pulseaudio[14764]: module-remap-sink.c: No
>> remapping configured, proceeding nonetheless!
> There appears to be a typo in your last remap where you have
> "channel_map=left_right" when I presume you mean "channel_map=left,right"
>> then, despite the fact that it says it's proceeding, it simply proceeds
>> to exit with no further log entries.
> Hmm, interesting. Can you run manually via pulseaudio -vvvv (with the
> appropriate --system argument - you'll have to run as root and it should
> drop privs to the "pulse" user)
>> So you may ask what I'm trying to accomplish.  I'm trying to downmix
>> stereo audio to mono before passing it off to the virtual sink mpd.001.
>> the reason is that I've got a blown speaker, that I've gotten rid of and
>> only one speaker left.  THis christmas music sounds terrible when you
>> can't hear alvin, or you can't hear simon and theodore.
> Oh Noes! :p
>> If you can help
>> me fix this existing config, or find a better way to downmix my music to
>> mono (actually mix l and r, not just one or the other) I'd be very
>> happy, and the children's christmas would be immeasurably merrier!
> One potentially easier (but maybe not as nice?) way would be to create a
> null sink with a single channel then use module-loopback sink to connect
> it's monitor to your real sink. It should automatically upmix the mono
> null sink to stereo on your real sink.... not 100% sure this will work
> but it should do.
> HTHs
> Col

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