Tone Clock

The Tone Clock, and its related Tone-Clock Theory, is a post-tonal music composition technique, developed by composers Peter Schat and Jenny McLeod. Because it emphasises the role of three-note chords (trichords or 'triads') in creating harmonic fields, it results in a high economy of musical intervals, despite the chromatic nature of its musical language.

While Tone-Clock Theory has many similarities to Allan Forte's pitch-class set theory, it places greater emphasis on the creation of pitch 'fields' from multiple transpositions and inversions of a single set-class, while also aiming to complete all twelve pitch-classes (the 'chromatic aggregate') with minimal, if any, repetition of pitch-classes. While the emphasis of Tone-Clock Theory is on creating the chromatic aggregate, it is not a serial technique, as the ordering of pitch-classes is not important, although it bears a strong similarity to the technique of 'serial derivation', which was used by Anton Webern and Milton Babbitt amongst others, in which a row is constructed from only one or two set-classes.

The term 'tone clock' (toonklok in Dutch) was originally coined by Dutch composer Peter Schat, in reference to a technique he had developed of creating pitch 'fields' by transposing and inverting a trichord so that all twelve pitch-classes would be created once and once only. Schat discovered that it was possible to achieve a trichordally partitioned aggregate from all twelve trichords, with the exception of the diminished triad (036 or 3-10 in Forte's pitch-class set theory). Schat called the 12 trichords the 'hours', and they became central to the harmonic organization in a number of his works.

In her as-yet-unpublished monograph 'Chromatic Maps', New Zealand composer Jenny McLeod extended and expanded Schat's focus on trichords to encompass all 223 set-classes, thus becoming a true 'Tone-Clock Theory'. She also introduced new terminology in order to 'simplify' the labelling and categorization of the set-classes, and to draw attention to the specific transpositional properties within a field.

The following terms are explained in McLeod's Chromatic Maps I:

New Zealand composer and music theorist Michael Norris has generalized the concept of 'tone-clock steering' into a theory of 'pitch-class tessellation', and has developed an algorithm that can provide tone-clock steerings in 24TET. He has also written about and analyzed Jenny McLeod's 'Tone Clock Pieces'.

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