Sound is usually thought of as a physical event out there in space, which must be distinguished from experiences of sound “in the head” or “ in the mind”. However all that the auditory sensors (our ears) detect are patterns of vibration at the eardrum, the experience of hearing sound which results from such vibrations are projected by the brain out there into space. Once we accept this, we can begin to thinks in terms of creating sound, which effects how the mind perceives vibrations, to entrain the brain with frequencies at which the mind functions to induce altered states of consciousness.

Auditory entrainment of cortical rhythms can occur through two different routes, by bursts of sound such as drum beats or one may achieve entrainment through the more subtle method of binaural beats. The range of the electrical rhythms of the human cortex is 0 Hz to about 40 Hz. Since humans have an auditory range of 20 to 20,000 Hz, it is not possible to directly entrain cortical rhythms below 20 Hz with pure tones. However, the phenomenon of binaural beats, an auditory brainstem response, allows the entrainment of frequencies below 30 Hz through the interaction of pure tones within the superior olivary nuclei. In 1839 H. W. Dove, a German experimenter, discovered the auditory effect of binaural beats (Oster, 1973). He found that when two different frequencies of sound were presented, one to each ear, a third frequency equal to the difference between the two frequencies was experienced. This third, binaural beat is actually the result of the interaction of the two primary tones within the auditory brainstem. For example, if a pure tone with a frequency of 400 Hz is presented to one ear and a second tone of 410 Hz is presented to the other ear, a third binaural beat with a frequency of 10 Hz will also be heard as a result of the interaction of the two frequencies. Binaural beats can be generated at frequencies below 40 Hz and may be used to entrain electrical rhythms of the brain to vibrate at the same frequency through the Frequency-following response within the human brain.