It works by putting a different frequency in your ear through regular stereo headphones. An ipod is 2 channel stereo, meaning there is actually two separate audio channels, one is each side of the headphones. The difference between the frequencies is known as a ‘beat’ frequency. Your brain waves are supposed to tune to the beat frequency.
I use to use the “Hemisync” meditation tapes. I had success using it to reach meditative states. I’ve also reached the same states without the tapes doing plain old meditation. It wasn’t a sure thing and still took practice.
My goal with using it was to meditate, not focus better, do better in school, or any of that crap. I did notice a carry over to my daily life from meditating regularly, which I haven’t been doing. It did make me more focused, de-stressed, and relaxed.
The binaural stuff is interesting, and I wanted to get an eeg machine to collect some data, but at the time it was prohibitively expensive, but I assume its much cheaper now.