By listening through stereo headphones to slightly detuned tones (i.e., two sound frequencies that differ by a small number of Hz), the brain hears the “difference” between the tones and will naturally speed up or slow down to match it. This is sonic brainwave entrainment in action. Facilitating a specific range of brainwave states may assist in many areas, including pain reduction, enhanced creativity, stress reduction, or accelerated learning.
The term binaural beat frequencies describes a neuroacoustical phenomenon that takes place when the brain perceives one tone in one ear with a slightly detuned tone in the other. As a means of measuring the difference between these two tones, the brain creates a third “phantom” tone, unheard elsewhere. This is known as a binaural (two-ears) auditory beat.
The use of BBFs is an ancient sonic technology. A few thousand years ago, someone discovered that two minutely detuned sounds create a third sound in the brain, and that our brainwaves slow down or speed up to match this natural third sound. The technology of modern computers allows us to become extremely precise in the application of these tones. The question becomes: What predominant brainwave state is most conducive to a desired activity? Beta, Alpha, Theta, or Delta?
Whereas filtration is the process of subtracting specific sonic frequencies from a soundtrack, creating the BBF effect is an additive process. De-tuned sine-wave tones are mixed into a soundtrack of music, nature, or white noise. Sometimes the two tones can be heard, other times they are sub-audio. This is a subjective decision on the part of the producer. For the greatest effect, headphones or stereo speakers placed in proximity to each ear are recommended.
The phenomenon known as binaural beats was discovered by the German researcher H. W. Dove in 1839. He found that binaural beating (an actual wah-wah effect similar to vibrato) took place when separate frequencies were introduced into each ear, for example, a tone of 100 Hz in the right ear and a tone of 108 Hz in the left. The brain strives to bridge the gap by creating a third tone that is the actual difference between the two; in this example, 8 Hz.
According to the biophysics authority Dr. Gerald Oster, the binaural beat exists only as a consequence of the interaction of auditory signals occurring within the brain. The sound of the binaural beat will only be heard with the participation of both ears. If one ear is covered and only one tone is heard, the brain will use normal auditory measurement senses to determine tone, amplitude, timbre, etc. The phenomenon of BBFs is a consequence of measurement.
This natural process of sonic measurement takes place not only in humans but in other animals as well. Simply put, as a sound wave passes around the skull, each ear gets a different portion of the wave. When the wave length of a sound signal is longer than the diameter of the skull, the brain hears the inputs from the ears as out of phase with each other. Binaural beat expert F. Holmes Atwater states that “it is this innate ability of the brain to detect phase differences between the ears that enables the perception of binaural beats.”
Do not drive or operate machinery while listening to recordings that contain binaural beats. For optimal results, headphones are recommended.
"Binaural Beat Frequencies" is excerpted from The Power of Sound, published by Healing Arts Press.
(c) 2001 Joshua Leeds. All rights reserved.