You should check into music that has "binaural beats" imbedded.
The human brain has 4 main operating frequencies:
Beta(12-30 Hz) - this is the frequency range for our alert, focused brain state we have during our daily lives.
Alpha (8-12 Hz) - mildly relaxed, light meditation, daydreaming brain state.
Theta (4-8 hz) - deep relaxation, meditation, creativity.
Delta (0.5-4 Hz) - deep, restorative sleep.
There is a phenomena known as "the frequency following response". This is when the brain syncs its frequency to external stimulus. In other words, if the brain is fed a audible stimulus of 4 Hz or below, it will sync up with it, and thus causing your brain to enter delta and causing one to go to sleep.
This is also known as "brainwave entrainment".
The problem is, we can’t hear a frequency of 4 Hz as a tone, we hear individual beats. The solution is to feed one ear with a frequency of say, 800 Hz, and the other ear with 804 Hz (only works with headphones). This creates an auditory illusion of the brain perceiving a third, pulsating "beat" equal to the frequency difference between the two tones. This is a binaural beat.
Most recordings with binaural beats will start at a higher frequency, something in the alpha range to begin relaxation, then slowly ramp down to delta to induce sleep.
Even more effective than just sound as a stimulus, is adding the same frequency visually.
There are various brands of light and sound machines that also include lightweight glasses that have LEDs, that flash the same frequencies as the binaural beats are playing in one’s ears.
I have one of these. Which I usually don’t use for sleep, but for meditation. I use programs that have a target of alpha or theta, which are the frequencies measured in experienced meditators.
30 minutes in my car on a particularly stressful work day, does wonders!
There are other brands of these at various price points.
Let me add, that these devices have inputs that you can use for injecting your own music to layer with the binaural beats, or things like affirmations, or other subliminal messages.
