When you read about so-called brainwave CDs, the phrase binaural beats turns up again and again. Binaural beats are crucial to older brainwave entrainment software like Hemisync and Holosync, and they're still an important ingredient even in up-to-date systems like the Brain Evolution System. In this article, we'll look at the science behind binaural beats.
Simple ideas are always best. Brainwave entrainment is based on a simple discovery. If you subject the brain to a rhythmic stimulus, it will tend to fall into step. With the right rhythm, it's possible to switch yourself into different states -- alpha (relaxed concentration), theta (meditation/creativity) or delta (sleep).
Now, for most people, sound is the best brainwave entrainment medium -- but the human ear isn't adapted for the very deep sounds needed to access low-frequency brain states. That's where beats come in.
If you play two widely different musical notes at the same time, they interact and you hear a chord. The characteristic sound of the chord -- warm, sad, angry -- is produced by the interaction of the different notes.
If you play two slightly different notes, you hear a special kind of interaction. It's as if you're listening to a single note, but with a superimposed 'throb' caused by the difference between the two sources. That throb is the 'beat note'. Beat notes are of interest to brain researchers for a number of reasons.
First, they're an effective way of getting a low-frequency stimulus. Need a 5Hz signal? No problem -- just play two notes of 500 and 505Hz at the same time, and there's your 5Hz 'carrier'.
Second, beat notes can have complex effects on the brain. Maybe you've heard a beat note when a guitarist is tuning up, or when two different engines are running in the same space? Now, imagine yourself listening to stereo headphones. Let's play those two slightly different sounds we mentioned earlier, one in each ear. As you might expect, you'll hear a beat note -- but no-one else does! The beat is produced inside your brain as it attempts to make sense of the different signals. This is a true binaural beat.
Binaural beats were first described by Heinrich Dove in 1839, but their full significance wasn't recognised until the early 70s, when Gerald Oster and Robert Monroe began to explore their effects on consciousness. Monroe adapted his pioneering work to form the basis of the Hemisync and its many successors from Holosynch onwards. All of these systems attempted to use binaural beat CDs to improve brainwave synchronization by presenting binaural beats that required collaboration between the two separate hemispheres of the brain.
These days the best brainwave entrainment systems use a whole spectrum of special sound techniques -- like the ones you'll find in the Brain Evolution System. But brainwave synchronization using binaural beats can still be an important part of the mix.