Since the upgrade to gstreamer 1.0, the loopback module doesn't work anymore.
I usually use it with:
$ pactl load-module module-loopback
ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: pulseaudio 1:2.1-0ubuntu3
ProcVersionSignature: Ubuntu 3.5.0-15.23-generic 3.5.4
Uname: Linux 3.5.0-15-generic x86_64
ApportVersion: 2.5.2-0ubuntu4
Architecture: amd64
Date: Tue Sep 25 19:13:06 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
SourcePackage: pulseaudio
UpgradeStatus: Upgraded to quantal on 2012-08-24 (31 days ago)
dmi.bios.date: 10/02/2008
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 1406
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: P5Q-PRO
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: Rev 1.xx
dmi.chassis.asset.tag: Asset-1234567890
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr1406:bd10/02/2008:svnSystemmanufacturer:pnP5Q-PRO:pvrSystemVersion:rvnASUSTeKComputerINC.:rnP5Q-PRO:rvrRev1.xx:cvnChassisManufacture:ct3:cvrChassisVersion:
dmi.product.name: P5Q-PRO
dmi.product.version: System Version
dmi.sys.vendor: System manufacturer
Well, it seems that gstreamer1.0 has nothing to do with that. After running:
$ apt-get remove libgstreamer1.0 gstreamer1.0
the problem still remains (I still have libgstreamer0.10).
I don't know if this is related to bug #1056334 since when I noticed the loopback module was broken, I tried to open the control center and found a crash.
Anyway, the module was working fine till yesterday so it's definitely coming from today's dist-upgrade. Let me know if I can provide more information.