BEATING SINUSOIDS AND PITCH CHANGES
Lloyd A. Jeffress · The Journal of the Acoustical Society of America · 1968
When two sinusoids of unequal frequency and amplitude are added, there is a frequency shift of the average tone during the moment when the beat cycle goes through a minimum. This fact is well known, but attempts to hear the corresponding change of pitch have generally been unsuccessful. By gating the tone and listening to only a short section, it is possible to hear the pitch difference between a sample taken during the minimum and one taken during the maximum.