The physical octave

The physical octave is an interval of two tones with frequency ratio 2:1. Humans perceive two tones one octave apart as similar. However, the perceptual octave is judged as perfect when the frequency ratio slightly exceeds 2:1. This phenomenon is called the « octave enlargement effect» (OEE). Theories of pitch perception attempted to explain it in terms of basic auditory mechanisms. However, aesthetical preference could also be involved. Up to now, the OEE in humans,is documented only by subjective data. The present study attempted to provide objective psychophysical data which would support that the OEE originates from basic auditory mechanisms rather than from aesthetical preference. Ten trained musicians were presented binaurally with two rapid melodic streams of pure tones. The streams had frequency distance ∆ varying around (and including) the physical octave and the task was to judge if the streams were exact transpositions of each other. We reasoned that performance should be optimal when ∆ is such that the tones of the two streams would sound maximally similar. An additional task of subjective identification of octave intervals was also performed. We hypothesized that if the explanation of OEE lies only on basic auditory mechanisms, then performance in the objective task should be best when ∆ would be an enlarged octave, while the subjective task should reveal preference for this ∆ too. The results partially supported this hypothesis, but did not exclude the additional possibility of an aesthetical preference for enlarged octaves. Perspectives for future experimentations are discussed.

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