IEMLADSPA is a plugin for ALSA that loads a LADSPA plugin, and allows control with any ALSA compatible mixer, e.g. alsamixergui.

IEMLADSPA uses any multichannel LADSPA Plugin for audio processing. It differs from similar plugins (e.g. 'alsaequal') as it will process both the recording and the playback streams in a single callback. Therefore, the number of channels must match the number of input channels + the number of output channels. E.g. a standard soundcard will have two (2) inchannels ("microphone") and two (2) outchannels ("speaker"), which add up to four (4) channels. The LADSPA plugin thus needs four audio in and four audio out ports.

This should allow to build echo-cancellers and similar devices via LADSPA.

IEMLADSPA is based on 'alsaequal' by Charles Eidsness:

http://www.thedigitalmachine.net/alsaequal.html

INSTALL

Download the latest version of the plugin and:

tar xvjf iemladspa-x.x.tar.bz2
cd iemladspa-x.x
make
sudo make install

DEPENDENCIES

• LADSPA-SDK

• ALSA Development headers and alsa-lib -- you may already have it as part of your linux distro, you can install in Debian (and derivatives, like Ubuntu) with

  sudo aptitude install libasound2-dev ladspa-sdk

USAGE

After installing you will have to modify your local .asoundrc alsa configuration file, adding something like this. If you're not using sound card 0 modify "plughw:0,0" accordingly.

ctl.ladspa {
	type iemladspa;
}
pcm.ladspa {
    type iemladspa;
    slave.pcm "hw:0,0";
}

You can adjust the control parameters of the plugin by using any alsa mixer, e.g.:

alsamixer -D ladspa

HELP

If you need any help just let me know, you can reach me at: https://github.com/iem-projects/alsa-ladspa-bridge/issues Please keep in mind that this is a development release and may have bugs.

More Advanced Stuff:

Check out the annotated asoundrc example file.

controls

The mixer-device ("ctl") and the audio device ("pcm") communicate via a controls-file (as given with the 'controls' setting in asoundrc). This file is a binary file that get's mmapped by both devices. As such the file is fragile, and cannot be shared between two different plugins, unless the two plugins are port-compatible. It can however be shared between devices that use the very same LADSPA-plugins (all instances will then be controlled simultaneously).

sample format

iemladspa currently only supports FLOAT and S16 format for communicating with the soundcard ("downstream") and the application ("upstream"). So you will probably need to pump the data through a plug to change the format.

pcm.<anothername>{
    type plug;
    slave.pcm <name>;
}

The LADSPA-plugin will always work on floating point samples.