The basic idea of brainwave entrainment is to use an external periodic stimulus to cause brainwave frequencies to fall into step with it at a frequency corresponding to the intended brain-state (for example, to induce sleep or meditative states). There is good evidence that the human brain has a tendency to change its dominant EEG frequency towards the frequency of a dominant external stimulus. Such a stimulus may be aural, as in the case of binaural or monaural beats and isochronic tones,or light (visual), or a combination of the two with a mind machine.
Types of brainwaves and the states associated with them are summarized below. Not all researchers distinguish gamma and epsilon waves as shown here.I first tried brainwave entrainment when I picked up three CDs at a second hand sale which used binaural beats to create brain entrainment “metamusic” targeting alpha and theta waves.
Monaural beats are derived from the convergence of two frequencies within a single speaker to create a perceivable pulse or beat. So playing a 400 Hz and 410 Hz tone simultaneously through one speaker will produce physical beats at 10 Hz.
Binaural beats, or binaural tones, are auditory processing artifacts, or apparent sounds, created within the brain when the same sounds are played in separate ears at slightly different frequencies. For example, if 300 Hz was played in one ear and 310 in the other, then the binaural beat would have a frequency of 10 Hz. A beating tone will be perceived, as if the two tones mixed naturally, out of the brain. The frequencies of the tones must be below 1,000 hertz for the beating to be noticeable. The difference between the two frequencies must be small (less than or equal to 30 Hz) for the effect to occur; otherwise, the two tones will be heard separately, and no beat will be perceived.
I meditated using the 3 CDs, produced by Hemisynch (The Monroe Institute) and found that it did facilitate the meditative state somewhat, although it was not a particularly significant change. I also experimented with isotones from http://www.iso-tones.com but could not detect any particularly noticeable effect. Isochronic tones are tones that are being turned on and off rapidly. They create sharp, distinctive pulses of sound.
Following a recommendation from Integral Institute (Ken Wilber) a couple of years ago, I experimented with some brain entrainment recordings from iAwake, which claims to use a number of additional techniques along with binaural beats to create powerful brain entrainment tools (http://www.iawaketechnologies.com/). I found these to be much more effective at moving me into alpha and theta states and indeed had several quite profound hypnagogic visions and meditative experiences using them.
These days I am not doing zazen every day, but I have been sitting around 3 times a week and usually, not always, using iAwake tracks for around 20-25 minutes to get to low alpha and delta. The tracks I have mainly used are:
Harmonic Resonance 1 Alpha
Harmonic Resonance 2 Theta
Harmonic Resonance 3 Delta, Epsilon
Profound Meditation Tier 1 Track 1 Beta—> Delta (1 Hz) in first 16.5 minutes
Profound Meditation Tier 1 Track 2 Delta (1 Hz —–> 0.3 Hz)
Profound Meditation Tier 2 Track 1 Same as Tier 1 but more intense strength
Profound Meditation Tier 2 Track 2 Same as Tier 1 but more intense strength
I usually spend 10 minutes on track 1 and then 15 minutes on track 2.
Occasionally I will use Audio Oxygen (mix of alpha, beta and gamma) or Digital Euphoria (Delta/Low Delta/Epsilon)