An Intelligent SP-MIDI Polyphonic Reduction Algorithm

Most current mobile phones only support SP-MIDI ring tones with specific polyphonic limits. Since most MIDI files contain music that was not composed with regard to polyphonic limits, a common problem in the mobile phone industry is conversion from MIDI to SPMIDI. However, simple MIDI to SP-MIDI reduction algorithms, such as note-stealing, may lose or interrupt important musical information. This paper presents a phrase stealing algorithm that drops the perceptually least important notes when reducing a MIDI file to SP-MIDI, and preserves the most important phrases. The phrase stealing algorithm connects notes into melodic lines before deciding which phrases to drop and which to keep. On a test set of nine musical examples, the system produced melodic lines with an average phrase length of 11 notes. Formal listening test results showed that listeners found the phrase stealing reduction very similar to the original, while the same listeners found the note stealing reduction only somewhat similar to the original