Time-point

In music a time point (point in time) is the beginning of a sound, rather than its duration. In serial music a time-point set, proposed in 1962 by Milton Babbitt, is a temporal order of pitches in a tone row which indicates the instants at which the notes start. This has certain advantages over a duration scale or row built from multiples of a unit, derived from Olivier Messiaen.

since duration is a measure of distance between time points, as interval is a measure of distance between pitch points, we begin by interpreting interval as duration. Then, pitch number is interpretable as the point of initiation of a temporal event, that is, as a time-point number. —Milton Babbitt

For example, a measure may be divided into twelve metrical positions. In 3/4 this equals sixteenth notes. The start of each position, or time point, may then be labeled, in order, 0-11. Pitches may then be assigned locations within measures according to their pitch set number, now their pitch/time-set number. In Babbitt's first example he shows subsequent numbers which ascend (0-11) as within the same measure (if four follows three it may sound immediately), and subsequent numbers which descend as in the following measure (if three follows four it must necessarily wait for the next appearance of time-point three).

Babbitt uses time points in Partitions (1957), All Set (1957), and Post-Partitions (1966), as well as in Phonemena (1969–70), String Quartets No. 3 (1969–70) and No. 4 (1970), Arie da capo (1974), My Ends Are My Beginnings (1978), and Paraphrases (1979).

Charles Wuorinen has also developed an approach to the time-point system, which differs greatly from Babbitt's.