An "octal arpeggiator", which uses the input from a standard MIDI keyboard to produce up to eight simultaneous, independent melodic lines. Each of the eight arpeggiators has separate controls for MIDI channel, program, motion algorithm, rhythm, and more. Arp-X8 combines these settings with input from the keyboard to produce music that can range from simple arpeggios to rich, rhythmically complex clouds of sound. Arp-X8 is fully interactive, with all output automatically recorded to a MIDI file for export to conventional sequencers. Multiple instances of Arp-X8 are automatically synchronized, and can sync to any other program or device that utilizes MIDI clock messages.