Running Ubuntu 17.10, when I plug an external USB Amp/Dac it is correctly recognized and I can play audio through it via aplay, but when I select it as my output sink from gnome sound, nothing happens: apps still output sound via the speakers.
In order to fix it I have to restart pulseaudio.
I've also found online that modifying /etc/pulse/default.pa, moving module-switch-on-connect.so loading before module-udev-detect.so, permanently fixes the issue.
ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: pulseaudio 1:10.0-2ubuntu3
ProcVersionSignature: Ubuntu 4.13.0-16.19-generic 4.13.4
Uname: Linux 4.13.0-16-generic x86_64
ApportVersion: 2.20.7-0ubuntu3.4
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/pcmC1D0p: sergio 1374 F...m pulseaudio
/dev/snd/controlC1: sergio 1374 F.... pulseaudio
/dev/snd/controlC0: sergio 1374 F.... pulseaudio
CurrentDesktop: ubuntu:GNOME
Date: Thu Nov 16 09:03:19 2017
InstallationDate: Installed on 2017-10-24 (22 days ago)
InstallationMedia: Ubuntu 17.10 "Artful Aardvark" - Alpha amd64 (20170926)
ProcEnviron:
LANGUAGE=en_GB:en
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_GB.UTF-8
SHELL=/bin/bash
SourcePackage: pulseaudio
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 06/08/2017
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.3.4
dmi.board.name: 0X41RR
dmi.board.vendor: Dell Inc.
dmi.board.version: A02
dmi.chassis.type: 10
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvr1.3.4:bd06/08/2017:svnDellInc.:pnPrecision5520:pvr:rvnDellInc.:rn0X41RR:rvrA02:cvnDellInc.:ct10:cvr:
dmi.product.family: Precision
dmi.product.name: Precision 5520
dmi.sys.vendor: Dell Inc.
modified.conffile..etc.pulse.default.pa: [modified]
mtime.conffile..etc.pulse.default.pa: 2017-11-15T18:42:36.359190
Your fix sounds good. I'll do some testing and see about getting it into Ubuntu properly.