ladspa plugins in .asoundrc and pulseaudio don't play nice

Bug #514902 reported by gergnz on 2010-01-30
This bug affects 1 person
Affects Status Importance Assigned to Milestone
alsa-lib (Ubuntu)

Bug Description

when using ladspa plugins in a custom .asoundrc when using pulseaudio applications fail to work with the following output:

~$ aplay tmp/foo.wav
ALSA lib pcm.c:2211:(snd_pcm_open_noupdate) Unknown PCM amp
aplay: main:608: audio open error: File exists

example .asoundrc:

pcm.!default {
  type plug
  slave.pcm amp

pcm.amp {
  type ladspa
  slave.pcm "plughw:0,0";
  path "/usr/lib/ladspa";
  plugins [
      label amp
      input {
        controls [ 6 ]

If I remove pulseaudio binary from /usr/bin and reboot (to start a fresh) the ladspa plugin works perfectly.

~$ lsb_release -rd
Description: Ubuntu 9.10
Release: 9.10

~$ apt-cache policy libasound2
  Installed: 1.0.20-3ubuntu6.1
  Candidate: 1.0.20-3ubuntu6.1
  Version table:
 *** 1.0.20-3ubuntu6.1 0
        500 karmic-updates/main Packages
        100 /var/lib/dpkg/status
     1.0.20-3ubuntu6 0
        500 karmic/main Packages

ProblemType: Bug
Architecture: amd64
Date: Sun Jan 31 08:53:17 2010
DistroRelease: Ubuntu 9.10
NonfreeKernelModules: vmnet vsock vmci vmmon
Package: libasound2 1.0.20-3ubuntu6.1
 PATH=(custom, user)
ProcVersionSignature: Ubuntu 2.6.31-17.54-generic
SourcePackage: alsa-lib
Uname: Linux 2.6.31-17-generic x86_64
XsessionErrors: (polkit-gnome-authentication-agent-1:3653): GLib-CRITICAL **: g_once_init_leave: assertion `initialization_value != 0' failed

gergnz (gergnz) wrote :
Daniel T Chen (crimsun) wrote :

Your asoundrc is invalid (incorrect syntax).

Changed in alsa-lib (Ubuntu):
status: New → Invalid
gergnz (gergnz) wrote :


please explain why the .asoundrc is invalid. This works OK without pulseaudio.


It only "works" because the parser wasn't strict enough to reject the
plughw pcm syntax.

However, let's look at the PA end: which device did you specify in
your ~/.pulse/ ?

gergnz (gergnz) wrote :

I don't have a

So some more digging and googling has returned some documentation, I can now make alsa work with pulseaudio. Though, reading further it would seem a smarter thing to potentially use pulseaudio to load the ladspa plugins.

so the plughw pcm syntax should just be 'slave.pcm "plughw";'?

I can now specify a device in my as such:
load-module module-alsa-sink device=ampd

have slightly changed the .asoundrc

# was !default
pcm.ampd {
  type plug
  slave.pcm amp

Thanks Daniel, it is very difficult to find appropriate documentation that is correct for your system.

Please close this bug.

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