JSFX

JSFX, short for Jesusonic Effects, is a domain-specific scripting language for real-time audio processing. It originated in the Reaper project and is implemented by Cockos in the JSFX host, where users can write audio effects and synthesizers in plain text. The language is designed to be lightweight, easy to learn, and tightly integrated with the host, allowing rapid DSP experimentation without compilation or external plugins.

Code in JSFX is organized into sections for parameter definitions, initialization, and per-sample or per-block processing. Parameters are exposed via sliders and toggles, providing a simple graphical interface in the host. The syntax is C-like but pared down for safety in real-time audio threads; scripts operate on multi-channel audio streams and maintain internal state between processing blocks.

Typical capabilities include orientation towards basic DSP building blocks: gains, filters, delays, envelopes, LFOs, oscillators, and simple stateful processors. Algorithms can read and write to delay lines, perform sample-accurate processing, and implement routing between inputs and outputs within the constraints of a single plug-in script. The host compiles and runs the script at load time and executes it during playback.

JSFX has an active community with a large repository of user-contributed scripts. Scripts are usually stored with a .jsfx extension and can be loaded directly into a Reaper project. While it offers rapid prototyping and portability, JSFX is not a full-featured plugin format; it omits some features of larger DSP environments and imposes real-time safety constraints.