Instructions: Hemi-Sync and Gateway Experience audio programs
Hemi-sync is a technology pioneered by Robert Monroe after having a near-death coupled with an out of body experience (OOBE). He set out to create technology to reproduce the out of body experience. Before beginning this journey, we encourage you to read his book trilogy Journeys Out of the Body, Far Journeys and Ultimate Journey.
If you were hooked up to an EEG, most likely your brain is operating in Beta (13Hz-25Hz), or Fully awake
If you were to deeply relax or meditate, you would find yourself in Alpha (7Hz-13Hz)
On your way to sleep, you are in Theta (4Hz-7Hz)
And while asleep, you find yourself in Delta (1Hz-4Hz), or Deep sleep
Your brain will also naturally tend to "entrain" on frequencies in the environment. We can, for example, get 4Hz into your head simply by flashing a light on and off 4 times per second. This will after a short time, appear on the EEG, and will alter your state of consciousness. "Trance" music operates in the 120-150bpm range, and when you line up the bass pulses and kick drums on a grid and work out the timing, it isn't called "Trance" for nothing!
HemiSync and the cerebral cortex
HemiSync uses a "trick" to get low frequences into your head, and for this reason it only works when played through headphones.
When two tones of slightly different frequencies are played in separate ears simultaneously, the brain perceives the creation of a new, third tone, whose frequency is equivalent to the difference between the two tones being played. If we, for instance, use a carrier frequency of 440Hz (A3 on a piano), to create a binaural beat of 4Hz we would de-tune the carrier by 4Hz between the left and right ears (so, 438Hz to the left ear, 442Hz to the right ear). Perceptually, you do not hear a difference in frequency, rather, a "beating" at 4Hz as the volume oscillates between full and null (the sinewaves are cancelling each other out in your cerebral cortex). If you listen to hemi-sync through loudspeakers, the frequency mixing occurs in the air and while you may hear a slight "wah wah wah" pulsing in the tone, you are not going to get the HemiSync effect.
Recently FOIA'ed documents from the CIA reveal their deep interest in the technology, and the physiogical and psychical effects it can produce, you are encouraged to look into the matter deeper.