Partially based on Wikipedia
The Bohlen–Pierce scale is a musical scale that offers an alternative to the octave-repeating scales typical in Western and other musics, specifically the diatonic scale. It was independently described by Heinz Bohlen, Kees van Prooijen and John R. Pierce in the 1970′s and 80′s.
Pierce, who, with Max Mathews and others, published his discovery in 1984, renamed the Pierce 3579b scale and its chromatic variant the Bohlen–Pierce scale after learning of Bohlen’s earlier publication. Bohlen had proposed the same scale based on consideration of the influence of combination tones on the Gestaltimpression of intervals and chords.
With a step size of approximately a three-quarter tone (146 cent), the middle-Eastern second degree, the scale has both the quality of a symmetrical scale of 13 steps per just twelfth (tritave), as well as a tuning which serves as a collection for subsets of pitches for the modes Bohlen identified in the 1970′s, which, for the most part, contain 9 unequal steps per twelfth. Bohlen added the labels H and J to the repertoire of the note names used for diatonic scales.
As the scale replicates at the interval of a just twelfth (3:1 ratio), it also lends itself to electronically stretched spectra based on a stretching index of 3. Approximating the partials to the pitches of Bohlen-Pierce scale reduces sensory dissonance and creates a coherence between the tonal and spectral dimensions of the tuning.
While early compositions in the Bohlen-Pierce scale mainly resorted to electronic sound generation, there is an increasing body of acoustic instruments capable of representing the scale such as the Bohlen-Pierce soprano clarinet, the BP pan flute, the BP guitar, a BP metallophone and a number of unusual instruments such as the Stredici.
The ever growing interest in the scale by composers and theoreticians has created many resources of which the most important ones should be listed here: