[pulseaudio-discuss] playback from loopback over network fades, dies every few minutes and then comes back

[Nick]

Greetings PulseAudio folks:

I'm trying to pipe audio between an amateur radio (basically a USB sound
card) hooked to a Raspberry Pi and my laptop over a local network. I've
built PulseAudio 6 on a Raspberry Pi B+ and set up module-tunnel-sink
and module-tunnel-source, and that's all functioning. I can record audio
on my laptop and it seems to work well. However, I need to be able to
monitor the sounds coming out of the radio live, so I set up a
module-loopback with the source set to the USB sound card on the RPi.

Here are the relevant bits in my system.pa config file:

load-module module-tunnel-sink server=laptop sink_name=xps rate=11025
load-module module-tunnel-source server=laptop source_name=xpss rate=11025
load-module module-loopback
source=TI_USB_Audio_CODEC-00-CODEC.analog-stereo latency_msec=100 rate=11025

I've downsampled because I'm trying to minimize bandwidth and don't need
hi-fi audio (after all, it's a ham radio). This works, but only for a
few minutes. Then, the audio from the loopback becomes choppy and
eventually fades out completely. It sits silently for about a minute
(sometimes more) and then comes back in full quality. A minute or so
later, the process repeats.

Some interesting tidbits:
1) Only the loopback fades. If I'm recording in an application on the
laptop from the networked tunnel source directly, it holds the signal
nicely the whole time (even during the fadeouts).
2) If I connect to my local network over a VPN, the loopback fading does
not occur at all.
3) The fading happens both on wifi connections and on hard-wired ones.
4) If I change the target of the loopback in pavucontrol's Playback tab
to something else and then back to my laptop speakers, it often stops a
fadeout and comes back strong for a minute or so (and then fades out
again).
5) The fading occurs both with the downsampled rate set on the loopback
and with the default.
6) This happens on multiple remix methods, including the default and
trivial.
7) This happens on both the Raspberry Pi B+ and on the Raspberry Pi 2.
CPU on the RPi2 is at about 20%.
8) The client (my laptop) has PulseAudio 4.0, not 6.0 like the server.

I've uploaded a recording of the fading phenomenon that you can listen
to here: http://partofthething.com/upload/pulseaudio-fadeout.mp3

I'm not sure what to do to continue debugging. Any suggestions?

Best regards,
-Nick