Cecilia is an audio signal processing environment. Cecilia lets you create your own GUI (grapher, sliders, toggles, popup menus) using a simple syntax. Cecilia comes with many original built-in modules for sound effects and synthesis.

Previously written in tcl/tk, Cecilia (version 4, deprecated) used the Csound API for communicating between the interface and the audio engine. Version 4.2 is the final release of version 4.

Cecilia5 has been now entirely rewritten in Python/wxPython and uses Pyo, an audio engine written in C and created for the Python programming language. Pyo allows a much more powerful integration of the audio engine to the graphical interface. Since it is a standard python module, there is no need to use an API to communicate with the interface.