Chords not required: Incorporating horizontal and vertical aspects independently in a computer improvisation algorithm

Most previous computer improvisation algorithms for tonal jazz create an output based primarily on the underlying chord progression. This approach may partly ignore melodic continuity often seen in transcriptions of traditional jazz artists. Here we suggest a different approach implemented as a computer algorithm that creates material solely based on probabilities related to past note choices. This approach aligns with theoretical work suggesting that stored motor patterns are the basis of improvised music. Our computer algorithm analyzes pitch and rhythm patterns from a given corpus and then creates improvisations using this information. We describe an example in which a corpus of 48 solos by jazz saxophonist Charlie Parker was used by our algorithm to create an improvisation of the same length. The artificial corpus contained pattern structures similar to that of the original corpus. In contrast, previous research by one of the authors showed that a chord-based computer algorithm generated an output with a pattern structure very different from that of the human improviser even though the same chord structure was used as input. Future work will add a vertical aspect to our model in which a given chord pattern influences note choices in addition to the current horizontal focus.