The ps13 Pitch Spelling Algorithm

In the ps13 pitch spelling algorithm, the pitch name of a note is assumed to depend on the local key and voice-leading. In the first stage of ps13, the pitch name implied for a note by a tonic is assumed to be the one that lies closest to that tonic on the line of fifths. The strength with which a pitch name is implied for a note is assumed to be proportional to the sum of the frequencies of occurrence, within a context around the note, of the tonics that imply that pitch name. In the second stage of ps13, certain neighbour-note and passing-note errors in the output of the first stage are corrected. An implementation of ps13, called PS13, spelt correctly 99.31% of the notes in a 195972 note test corpus, C. A post-processing phase was added to PS13 in which the pitch names computed by PS13 are transposed by a diminished second if this brings them closer on the line of fifths to the pitch names of the notes in their vicinity. This version of the algorithm spelt 99.43% of the notes in C correctly. When the second stage was removed altogether from PS13, 99.44% of the notes in C were spelt correctly. The ps13-based algorithms achieved higher note accuracies than the algorithms of Temperley, Longuet-Higgins, Cambouropoulos and Chew and Chen on both C and a “noisy” version of C containing temporal deviations similar to those that occur in MIDI files derived from human performances.