LADSPA

LADSPA stands for Linux Audio Developer's Simple Plugin API. It is a standard for writing and loading audio effects and synth plugins for use in digital audio workstations and other audio processing applications on Linux and other Unix-like systems. The API is designed to be simple, lightweight, and portable, enabling plugin authors to implement their effects as shared libraries that can be loaded by hosts at runtime.

Design and scope: LADSPA defines a compact set of entry points that a plugin must implement. A plugin provides a descriptor that reports its name, number of ports, and port types, along with functions to instantiate the plugin, connect the host’s audio and control ports, activate, process audio blocks, and clean up. Plugins expose ports of two main kinds: audio ports (for inputs and outputs) and control ports (for parameters such as gain or cutoff). The host allocates buffers, maps ports, and calls the plugin's run function to process audio frames.

Usage and ecosystem: LADSPA plugins are distributed as dynamically loadable libraries and are discovered by hosts through directories or plugin listings. The format has seen wide adoption in Linux audio software and is supported by many hosts, including Ardour, Audacity, Qtractor, and Carla. The standard remains in use due to its simplicity and broad compatibility, even as more modern extensions and replacements have emerged.

Relation to LV2: LV2 is a newer plugin standard that builds on similar concepts but adds greater extensibility and features. LV2 is often described as a successor to LADSPA, though LADSPA continues to be used widely for its straightforward design and compatibility.