We describe an intermediate language designed as a medium-level internal representation of programs of the interactive music system Antescofo. This representation is independent both of the Antescofo source language and of the architecture of the execution platform. It is used in tasks such as verification of timings, model-based conformance testing, static control-flow analysis or simulation. This language is essentially a flat representation of Antescofo's code, as a finite state machine extended with local and global variables, with delays and with concurrent threads creation. It features a small number of simple instructions which are either blocking (wait for external event, signal or duration) or not (variable assignment, message emission and control).