Scientists and psychologists at the Monroe Research Institute developed and patented the use of Binaural Tones in 1965. These tones were found to be effective in synchronising brain-waves to match states of consciousness associated with creative visualisation, accelerated learning and astral projection thus assisting novices in the field of meditation to more easily achieve these goals.
An interesting thing about traditional African trance music is that because the musicians create a complex weave of polyrhythms and melodies by playing in the spaces between, there is on average an incredible 520 tone pulses per minute of 8 tone pulses per second in the music. This 8 pulse per second (8 Hz) signal is the most common frequency used in modern meditation technology and mind machines.
The 8 Hz pulsing matches the brain rhythms commonly referred to in psychology as the 'Theta Window'