Isorhythm (Greek: "the same rhythm") is a composition technique used to generate melodic material where events are constructed by iteratively pairing together single rhythmic and melodic objects parameters independently considered. Isorhithmia enables the systematized generation of melodic statements by assuming a melody as a sequence of events, where events are assembled by consecutively pairing items from two separate lists (a list as an ordered collection of items).
The inner working principles of isorhithmia can be described as manipulation of lists. Two lists, one list as an ordered collection of duration-values, named talea (as in "cut" or "slice of time", in Latin), and a second list list, termed color (Latin: "tone”), as an ordered collection of note-values. Each list is looped separately and in parallel. For each cycle, loop through both lists, pairing consecutively one element from talea with one element from color. If one of list is shorter in length than the other, it will run out of elements before the larger list has finished, in which case, the list is looped, cuing it back to the beginning. As example, let us assume the following talea (A B C) and color (W X Y Z). At the end of the first cycle, the output should be: ((A W) (B X) (C Y)). The second cycle's output, however, witnesses the first overlap of the two lists ((A Z) (B W) (CX)), where the first event results from pairing the first duration-value in the talea, A, with the last value included in the color, Z.
Using lists with different sizes became a common trait using this type of algorithms. The overlapping of lists precludes the two lists from re-aligning at the end of the each loop. With the list overlapping, at each repeat talea and color will coincide at different locations of the lists before finally reaching the end of all combinations. In the opening of Kyrie I of the Messe de Notre Dame by Guillaume de Machaut (1300-1337), there is a 28-note color arranged into seven taleae. Each talea includes four note-durations which after seven instantiations of the talea lay-out a temporal grid for all 28 notes of the color to be instantiated.
The use of isorhythmic type of algorithms has been omnipresent through numerous cultures and traditions, ranging from thirteenth-century French music to twentieth-century "avant-garde", classical Indian music, among others.
The inner working principles of isorhithmia can be described as manipulation of lists. Two lists, one list as an ordered collection of duration-values, named talea (as in "cut" or "slice of time", in Latin), and a second list list, termed color (Latin: "tone”), as an ordered collection of note-values. Each list is looped separately and in parallel. For each cycle, loop through both lists, pairing consecutively one element from talea with one element from color. If one of list is shorter in length than the other, it will run out of elements before the larger list has finished, in which case, the list is looped, cuing it back to the beginning. As example, let us assume the following talea (A B C) and color (W X Y Z). At the end of the first cycle, the output should be: ((A W) (B X) (C Y)). The second cycle's output, however, witnesses the first overlap of the two lists ((A Z) (B W) (CX)), where the first event results from pairing the first duration-value in the talea, A, with the last value included in the color, Z.
Using lists with different sizes became a common trait using this type of algorithms. The overlapping of lists precludes the two lists from re-aligning at the end of the each loop. With the list overlapping, at each repeat talea and color will coincide at different locations of the lists before finally reaching the end of all combinations. In the opening of Kyrie I of the Messe de Notre Dame by Guillaume de Machaut (1300-1337), there is a 28-note color arranged into seven taleae. Each talea includes four note-durations which after seven instantiations of the talea lay-out a temporal grid for all 28 notes of the color to be instantiated.
The use of isorhythmic type of algorithms has been omnipresent through numerous cultures and traditions, ranging from thirteenth-century French music to twentieth-century "avant-garde", classical Indian music, among others.
