The finite state transducer (FST), a type of finite state machine that maps an input string to an output string, is a common tool in the fields of natural language processing and speech recognition. FSTs have also been applied to music-related tasks such as audio fingerprinting and the generation of musical accompaniment. In this paper, we describe a system that uses an FST to generate harmonic accompaniment to a melody. We provide details of the methods employed to quantize a music signal, the topology of the transducer, and discuss our approach to evaluating the system. We argue for an evaluation metric that takes into account the quality of the generated accompaniment, rather than one that returns a binary value indicating the correctness or incorrectness of the accompaniment.