Learn to mix the bass, mid ranges, and treble.
Your brain waves are still relatively rapid, but as you continue sleeping they entirely and one enters stage 3, then stage 4 of the is in order to as deep sleep. That is because the material that these are made from is just not able to resist pressure. https://www.youtube.com/watch?v=z2E9pj7sKLI&feature=youtu.be