I'll add something here, and if folks are interested I'll carry on later.
Listening to audio frequencies as a means of achieving altered states of consciousness is not new. It is accomplished by means of 'binaural beats' which takes advantage of the signal differencing function in your superior olivary nucleus, located in your brain stem. This effect was discovered in 1839 by Heinrich Wilhelm Dove.
Perhaps the most well-known (and well-funded) formal investigation of this phenomenon was pursued by the Monroe Institute beginning in the 1970's. For those of you here who have out of body experiences (OBE's), you'll probably recognize the name Robert Monroe, who founded the Institute. If you haven't heard of Monroe, and you're fooling around with OBE's - I strongly encourage you to get caught up on your reading.
Last January I spent a week at the Monroe Institute which amounted to an intensive program of daily excursions using Hemi-Sync frequencies to achieve a host of different altered states of consciousness. They call it the 'Gateway Experience'. Just for the record, I'm a happy customer and will go back soon for other programs they offer.
If there's any question about whether you're being hypnotized while listening to audio recordings of this type, I'll tell you the answer is almost certainly yes. In fact reaching the hypnagogic state is pretty basic and an important step to reaching much deeper states. It's also quite easy to embed post-hypnotic suggestions and directions in those audio recordings using any number of methods that aren't easy to detect. So, my point is that you'll want to be very careful to verify who it is that has produced these audio sequences, what they might contain and what subliminal effects they may have.
I don't mean to frighten anyone, just the opposite. I'm convinced this technique is a legitimate way to explore. But don't be naive either. If you'd like to get caught up quickly on what was accomplished at the Monroe Institute, this is the book:
"The Journey of Robert Monroe: From Out-of-body Explorer to Consciousness Pioneer" by Ronald Russell