http://en.wikipedia.org/wiki/Binaural_beats
I am curious about this part:
http://en.wikipedia.org/wiki/Binaural_beats#Brain_waves

Not in the sense of being a person who wants to use 'artificial' means to change my own state of mind. Just a general curiousity. (Why do I feel the need to point that out? Because the one person I know really into this liked to take lots of drugs and eventually developed schizophrenia.)

Not so curious about this:
http://binaural.com/binbb.html

Was wondering does a difference of sound of about 10Hz ever 'naturally' occur between the left and right ear. And think it must almost never occur. The frequency distance between notes in the 12 tone traditional scale is too much. Except for very low bass (where the step is less). But still probably never does two such different notes occur with one to the far right and one to the far left.

But, still I think it would be pretty easy to modify a song so that it had some binaural beat aspects to, where the freq difference was in the 10 to 40Hz range... Simply by taking a completed rendered track and pitch shifting it up 20 cents and to the far right. Then a second completed rendered track pitch shifted down 20 cents and to the far left. Guesstimating 20 cents taking into consideration a very rough estimate of an average note in the mid 4th octave where the frequency step is 16, 20 Hz or so. Take roughly half of that to try to entrain a brainwave frequency on the edge of sleep around 8Hz or so.

But this effect, whatever soothing effect it might possibly have, I think would be drowned out by the simple consanance/dissonance, synesthesia, etc of the music/sounds. For the heck of it I modified something where I put to the far left and right: 20 cents down, 20 cents up, a whole octave down and a whole octave up plus normal right down the middle.

At first I felt soothed just in that there are far more voices then there were originally. And the more the better to me. (more life, more points of view, a richer world). Also it was just new and thus refreshing.

To my wife it sounded awful. But it always does.

There is a beating to it. (which isn't the goal.)
http://www.phy.mtu.edu/~suits/beats.html
But it seems to be caused by the octave up and down tracks. Although I can also create such beating by taking two wavelengths that are 5, 10Hz, etc different. The faint beating of this track hasn't gotten annoying yet. Although it's surely on a different time than the 134.5 BPM of the song file.

This is all a probably silly thing but the wiki article did fascinate me. I work in an epilepsy unit and can sit there and monitoring people's brainwaves (although that's not my job). I can tell just by looking at their brainwaves whether they're asleep of awake (or having a seizure). Perhaps this concept could be used for epileptic seizures?