Theta brain waves occur when you’re sleeping or dreaming, but they don’t occur during the deepest phases of sleep. They may occur when you’re drifting off to sleep or suspended in that light phase of sleep, just before you wake up.
Theta brain waves can also occur when you’re awake, but in a very deeply relaxed state of mind; a state that some may describe as “autopilot.” However, if you experience high levels of theta waves while you’re awake, you might feel a little sluggish or scattered.
Experts believe that theta waves are important for processing information and making memories. And, as researchers learn more about how they work and how they’re linked to different types of learning, this knowledge may come in handy when determining the best way to help people learn.

Theta waves have a frequency from 4 to 8 hertz. Humans can't hear a theta wave, and regular speakers can't produce such a low frequency, so the wave is created by playing a slightly different frequency in each ear. The result is a theta wave. For best results, use headphones.