A user interface for a virtual musical instrument presents a number of chord touch regions, each corresponding to a chord of a diatonic key. Within each chord region a number of touch zones are provided, including treble clef zones and bass clef zones. Each treble clef touch zone within a region will sound a different chord voicing. Each bass clef touch zone will sound a bass note of the chord. Other user interactions can modify or mute the chords, and vary the bass notes being played together with the chords. A set of related chords and/or a set of rhythmic patterns can be generated based on a selected instrument and a selected style of music.