Tone clock

The tone clock, and its related compositional theory tone-clock theory, is a post-tonal music composition technique, developed by composers Peter Schat and Jenny McLeod. The purpose of the tone-clock is to consistently order chromatic pitches into 12 triads where each pitch is used only once. Music written using tone-clock theory features a high economy of musical intervals within a generally chromatic musical language. This is because tone-clock theory encourages the composer to generate all their harmonic and melodic material from a limited number of intervallic configurations (called "intervallic prime forms", or IPFs, in tone-clock terminology). Tone-clock theory is also concerned with the way that the three-note pitch-class sets (trichords or "triads" in tone-clock terminology) can be shown to underlie larger sets, and considers these triads as a fundamental unit in the harmonic world of any piece. Because there are twelve possible triadic prime forms, Schat called them the "hours", and imagined them arrayed in a clock face, with the smallest hour (012 or 1-1 in IPF notation) in the one o'clock position, and the largest hour (048 or 4-4 in IPF notation) in the 12 o'clock position. A notable feature of tone-clock theory is tone-clock steering: transposing or inverting hours so that each note of the chromatic aggregate is generated once and once only.