Perception of Two-Tone Octave Complexes

Two pure tones with a frequency ratio of 1 : 2 and an adjustable phase relation, if presented simultaneously to the ear, can give rise to perceptual alterations due to a change of the phase. In this investigation, the level of the higher-frequency component was always chosen at least 20 dB below the level giving “best beats” at a given level of component 1. The white-noise masking level, the loudness and the pitch of the higher-frequency component were measured as a function of the phase under these conditions.

Experiments were also performed to investigate the masking of pure tones for test tone frequencies about an octave above that of the masker.

One frequently accepted explanation of phase effects like those investigated here is based on the idea of “aural harmonics”, the postulated products of mechanical distortion in the ear due to a strong lower-frequency component. Another explanation relates the phase effects to the variations in the waveform of the superimposed sinusoids of the two components.

The experimental results described in this paper do not offer conclusive evidence for or against either of these two hypotheses.