FluidSynth LADSPA Interface

The LADSPA (Linux Audio Developer's Simple Plugin API) binding can be used to route the FluidSynth audio output through any number of LADSPA plugins. As the name implies, it is only available on Linux.

Configuration

To configure and compile FluidSynth with LADSPA support, make sure you have the LADSPA SDK (basically the ladspa.h header file) installed. Then enable LADSPA when calling cmake:

cmake -Denable-ladspa=1 <path-to-source>

You should see LADSPA support: yes in the cmake output.

To enable the LADSPA engine, use the synth.ladspa.active setting when starting FluidSynth:

fluidsynth -o synth.ladspa.active=1 ...

Signal Flow

The LADSPA effects unit runs immediately after the internal reverb and chorus effects have been processed. When no plugins have been configured, the effects unit is dormant and uses no additional system resources.

When at least one plugin is configured and the engine is activated, the rendered audio is passed into the LADSPA effects unit, each plugin is run in the order that they were created and the resulting audio is passed back into FluidSynth (and from there to the sound card or other output).

Loading and Connecting Plugins

Currently the only way to configure the effects unit is via the FluidSynth shell or via a config file.

Example Setups

All examples assume that your LADSPA_PATH environment variable points to the directory containing the plugin libraries (e.g. /usr/lib/ladspa).

Single Plugin

The following loads the delay.so plugin library from the LADSPA SDK and instantiates the delay_5s plugin from that library. It connects the main left channel output from FluidSynth with the plugin input, the main left channel input to FluidSynth with the plugin output. It also sets the two control ports of the plugin to example values and starts the engine.

ladspa_plugin delay.so delay_5s
ladspa_port Input < in1_L
ladspa_port Output > out1_L
ladspa_port Delay = 1.0
ladspa_port Dry/Wet = 0.5

ladspa_start

The audible effect should be an untouched right channel and a slightly lower volume on the left with a delay effect of 1 second on top.

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