Melodic octave tuning; separable dimensions of perception

Ascending and descending digitally synthesized pure-tone melodic octaves in the range 250–1500 Hz, varying width from 1180¢ to 1220¢ were presented to nine highly musical subjects who were asked to judge (1) degree of octave mistuning, and (2) whether the second tone of the pair was sharp or flat. Results confirm the existence of so-called “octave stretch” previously reported in the literature. However, the two tasks were found to be perceptually dissimilar in degree of octave stretch, variability, and dependence on register. Consistent with results of Lindqvist and Sandberg (VIIth Int. Congr. Acoust., 1971] preferred “octave stretch” for the “sense of mistuning” judgments was very small (about 2.5¢) for low register octaves. An additional significant finding was that melodic octaves whose second tone was flat relative to an adjudged “in tune” octave were called more “mistuned” than octaves whose second tone was equally sharp. Together, these results imply that perception of octave tuning does not amount to a one-dimensional judgment of log frequency difference, but is multidimensional in nature.