[pulseaudio-discuss] Crackling sound with module-loopback

Davíð Steinn Geirsson david at dsg.to
Mon Apr 2 10:40:54 PDT 2012

Hi all,

I'm having a problem using module-loopback. I'm trying to take line-in
audio in on machine A, stream it using pulseaudio to machine B and play
it there. However I get crackling sound on the remote.

The network streaming is no problem, I can play sounds on machine A and
they will play through machine B's speakers without crackling.

I can sort of get the behaviour I want now with "pacat -r | pacat -p" on
machine A, but pacat has it's own internal buffer so the latency using this
is bad (1-3 seconds depending on the value of --latency-msec).

So I want to use module-loopback to have pulseaudio automatically connect
my line-in source to the network sink.

I do this with (on machine A):
pacmd load-module module-tunnel-sink server= rate=48000 channels=2
pacmd load-module module-loopback source=alsa_input.pci-0000_00_05.0.analog-stereo sink=tunnel. latency_msec=80 rate=48000 channels=2

Using this, I get sound (usually - but that's a different problem). However
the sound is very crackly. It ranges from "slight crackle that's annoying" to
"I can't even tell what song is playing".

I have default-sample-rate = 48000 in my daemon.conf. I originally did not
specify a rate in daemon.conf nor for the modules but it had the same effect.

Any ideas what I could be doing wrong? Any help would be greatly appreciated.

I'm running an ubuntu-provided pulseaudio (package version is 0.9.22~0.9.21+stable-queue-32-g8478-0ubuntu14, pulseaudio --version identifies as pulseaudio 0.9.21-63-gd3efa-dirty). The kernel version is 2.6.32 (2.6.32-38-server).

I can try to update if that's necessary but I assume this is probably a
configuration issue on my end.

Best regards,
Davíð Steinn Geirsson
david at dsg.to
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