MT is a melody transcription system that accepts acoustic input, typically sung by the user, and displays it in standard music notation. It tracks the pitch of the input and segments the pitch stream into musical notes, which are labelled by their pitches relative to a reference frequency that adapts to the user's tuning. This paper describes the signal processing operations involved, and discusses two applications that have been prototyped: a sightsinging tutor and a scheme for acoustically indexing a melody database.