I'm writing to provide information regarding the practical application of entrainment. The concept is indeed tantalizing. However, there is an important fact to consider regarding the reproducibility of brain wave frequencies is audio form.
Delta, theta, alpha frequencies range from 4hz to 12hz. These three are observed in states of relaxation to deep sleep. While it is possible to generate such low frequencies using a synthesizer, it is nearly impossible to reproduce with most, if any, speaker. Headphones can produce low frequencies down to 20hz or so, but the decibel output is negligible, as well as being above the desired delta, theta, alpha range.
Therefor, recordings that advertizing delta, theta, alpha reproduction are in fact useless.
It's a cool concept though.
I do this with the free software Audacity. I insert a 45 minute tone at, say, 211.44hz. When the software is finished rendering it, I them have it produce a tone for the same length of time, but at 218.94hz. Both frequencies are now overlapping. I then make it so that the first time plays only on the left while the second tone plays only on the right and then export it to mp3 format, which I can sync to any media player. Now, while listening on headphones (not speakers, this truck won't work on speakers) my mind reinterprets the tones and, after a little while, entrains to 7.5hz, which is the difference between 218.94 and 211.44.
I realize that I'm responding to a year old post, but I just joined the forum today and wanted to add my input.
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