The Percussion Interface (PI) and PI Expander are a pair of Eurorack modules that generate gates and envelopes from acoustic drums, samplers, drum machines, and virtually any audio source.

Converting microphone, instrument, line and modular signals into CV and clock/gate signals, the PI and PI Expander are suited for synchronizing sequencers or other modules to the rhythm of an audio track or live percussion. The modules can simultaneously be used as a pre-amp for microphones or line-level signals, while generating inverted envelopes useful for side-chaining. The PI module contains all the core functionality and can be used without the Expander to conserve space. The Expander requires the main PI modules and adds three gain stage options, a modular-level audio output jack, a 1/4" (6.35mm) input jack, and envelope attenuation capabilities. The two modules are only sold together, they are not available separately.