|LADSPA (Linux Audio Developers Simple Plug-in API) is an audio plug-in standard originally developed on Linux, but which can be ported to Windows and Mac too. Audacity has built-in support for LADSPA plug-ins.
Writing LADPSA plug-ins
Audacity behaves as an excellent LADSPA host. Just read up about LADSPA, and make your plug-ins correctly. As a starting point, look at some LADSPA Plugin Developers' Documentation and some example plug-ins. Keep in mind that Audacity "runs" the plug-in multiple times with some specific number of samples. So, don't assume that your plug-in will get the entire selection the first time.
Obtaining LADSPA plug-ins
- Windows and Mac: Any LADSPA plug-in compiled as a Windows .dll or Mac .dylib shared library will work on these platforms. An extensive set of "swh" plug-ins by Steve Harris is available for Windows and Mac.
- GNU/Linux: The easiest and recommended method of obtaining pre-compiled LADSPA plug-ins is to install them using the download repository or package manager for your distribution of Linux. Other LADSPA plug-ins can be found online such as at http://linux-sound.org/ladspa.html. However in some cases downloading plug-ins from external sites will require you to compile the plug-ins yourself, or at least manually install them yourself.
Using LADSPA plug-ins
On GNU/Linux, if you have the ladspa-sdk installed, you can run listplug-ins from a terminal to list all plug-ins in your LADSPA_PATH.