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

[gergnz]

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
libasound2:
  Installed: 1.0.20-3ubuntu6.1
  Candidate: 1.0.20-3ubuntu6.1
  Version table:
 *** 1.0.20-3ubuntu6.1 0
        500 http://mirror.aarnet.edu.au karmic-updates/main Packages
        100 /var/lib/dpkg/status
     1.0.20-3ubuntu6 0
        500 http://mirror.aarnet.edu.au 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
ProcEnviron:
 LANGUAGE=
 PATH=(custom, user)
 SHELL=/bin/bash
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

[Daniel T Chen (crimsun)]

Your asoundrc is invalid (incorrect syntax).

[gergnz (gergnz)]

Daniel,

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

Greg.

[Daniel T Chen (crimsun)]

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/default.pa ?

[gergnz (gergnz)]

I don't have a default.pa.

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 default.pa 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.