How to Attach LADSPA Plugins to Ecasound Chains

Ecasound is a versatile command-line multitrack audio processing tool that supports real-time audio routing, recording, and effects processing. Integrating Linux Audio Developer's Simple Plugin Architecture (LADSPA) plugins into an Ecasound signal chain allows users to apply a wide variety of audio filters, dynamics processors, and effects. This guide details the exact command-line syntax required to attach LADSPA plugins using both plugin labels and unique numerical identifiers.

The LADSPA Plugin Operator Syntax

In Ecasound, effects and processors are attached to the currently selected audio chain using operators. LADSPA plugins are attached using either the -el (by label) or -eli (by unique ID) option.

Attaching by Plugin Label (-el)

The standard syntax to load a plugin using its textual label is:

-el:plugin_label,param1,param2,...

• plugin_label: The unique alphanumeric name assigned to the plugin in its descriptor.
• param1,param2,...: A comma-separated list of values for the plugin's control input ports.

Attaching by Plugin ID (-eli)

If you prefer to target a plugin by its numeric LADSPA identifier, use:

-eli:plugin_id,param1,param2,...

• plugin_id: The integer ID assigned to the plugin.

Command-Line Execution Examples

1. Applying a Lowpass Filter by Label

To process an audio file (input.wav) through the standard LADSPA single-pole lowpass filter (lowpass_iir) and send the output to your soundcard:

ecasound -i:input.wav -el:lowpass_iir,1000,1 -o:alsa

In this command:

• -i:input.wav sets the input source.
• -el:lowpass_iir,1000,1 attaches the lowpass_iir plugin with a cutoff frequency of 1000 Hz and stage parameter set to 1.
• -o:alsa routes the output to the default ALSA device.

2. Specifying Chain Assignment

When working with multiple chains, ensure you explicitly select the chain using -a:chain_name before adding the LADSPA operator:

ecasound -a:1 -i:input.wav -el:amp_mono,2.0 -a:1 -o:output.wav

This applies a mono amplifier plugin (amp_mono) with a gain multiplier of 2.0 directly to chain 1.

Discovering Plugin Labels and Parameters

Before attaching a LADSPA plugin, you must know its accepted label and the order of its control input parameters. You can inspect installed LADSPA plugins using external utility commands:

• listplugins: Displays a list of all installed LADSPA plugin libraries and their member plugins.
• analyseplugin <plugin_name>: Displays the label, unique ID, and required input control ports for a specific plugin library.