This explanation is supported by observations made with a constant source rotating around the head of a listener. They are explained by assuming that the sound appears louder when the phase relations are such that it is normally best localized in the position toward which the attention is directed. Fast beats (more than 1 per sec.) are generally recognized as an intensity fluctuation. For example, if you are hearing a sound that is at. Such maxima are explained as the result of one's interpreting the sound as louder when localization is more definite. Binaural beats is when your brain hears two different tones in each ear, that are a different frequency. If the beats are slow (less than 1 per sec.) they are generally recognized as an alternate right and left localization, though some observers may report one or more intensity maxima during the beat cycle. The evidence indicates that these beats are not due to cross conduction but are of central origin and the result of the sense of binaural localization of sound by phase. Data obtained with 22 observers are summarized. Subjective binaural beats are heard for frequencies below 800 or 1000 cycles when the tones at the two ears have about the same amplitudes, differing by not more than 25 TU. These beats are heard because the louder tone is conducted through the head to the ear of the weaker tone and the two tones there are about equally loud. For telephone receivers as sound sources, this difference for best beats is about 55 TU and for the same receivers supplied with sponge-rubber cushions about 62 TU.
Objective binaural beats are heard for most values of f within the audible frequency range, provided there is the proper difference in amplitude between the two tones. By introducing a tone of frequency f into one ear and another tone of frequency f + N into the opposite ear, where N is less than 5 or 6 cycles, two kinds of binaural beats are obtained.
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