What has been learned is that it is possible to use external stimulation to alter a person’s brainwave frequencies. This was reported in 1973 by biophysicist Gerald Oster of Mount Sinai Hospital in New York City, published his article "Auditory Beats in the Brain" in Scientific American. He found that when different sound frequencies are delivered to the brain separately through each ear, the two hemispheres of the brain function together to "hear" not just the external sounds, but a third phantom signal is created as well – binaural beats.

He found that our brainwaves can be entrained to synchronize with certain external stimulus; this is called a “frequency following response.” Research has shown that at first parts of the brain and, in time, large areas of the brain begin to resonate and become active while experiencing the frequency following response. Binaural Beats have proven to be an excellent tool for entraining specific brainwave states.

As an example, someone who is stressed and anxious, but willing to relax, could listen to a binaural beat sound in the Alpha range, and would slowly start to change over time from 40Hz to a more peaceful and relaxed state where their brainwaves were predominantly at 10Hz.

How Binaural Beats Are Made
If a steady tone is played into a person's left ear at 200Hz, and their right ear is played a steady tone of 210Hz, those two tones combine to make a binaural beat of the difference of the two tones, which would be 10Hz. When using stereo headphones, the left and right sounds do not mix together until in your brain. This brain-created beating sound is incredibly effective for entraining brain waves and thus altering states of consciousness!

Try it
Put on your headphones and listen to this sample.
First you’ll hear a 200Hz tone in your left ear, and then a 210Hz tone in your right. Then the two will be played together so that you can experience the binaural beating at ten cycles per second, or 10Hz. Next you’ll hear a 200Hz tone in your left ear, and a 205Hz tone in your right, followed by a 5Hz binaural beat example. Last you’ll hear a 200Hz tone in your left ear, a 202Hz tone in the right and then a 2Hz tone example.