I wasn't sure I believed that they really made you sleepy so I burned that music along with other classical music onto a cd and gave them to my massage therapist. I asked her to let me know if any of the tracks made her sleepy (of course I told her there was a possibility she'd get sleepy and asked if it was ok). Interestingly, all of the tracks with the delta waves were the ones she picked as making her and her clients sleepy.