Proportional relationships of simple numbers were commonly used in architecture during the Renaissance period. These proportional relationships were based on the primary musical consonances of the Greek musical system: the octave (2:1), fifth (3:2), and fourth (4:3). In a similar manner, Obrecht uses the proportional relationships created by periods of rest and the last notes of the cantus firmus segments. These proportional relationships are found in the same voice as the cantus firmus, and appear when the statements of the cantus firmus segments are absent. Together with the statements of the cantus firmus segments, these proportional relationships provide the entire form and structure for the various parts of Obrecht's segmentation masses.
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