By means of a difference tone (a third tone created by the combination of two detuned sound sources) a frequency is perceived by the human ear. These ultra low tones in the 4-7 HZ range are the same as the ones naturally produced in the brain during meditation. Through the process of entrainment, the tendency of two bodies to move together in vibration, the meditative state can be reinforced. These pieces have these tones (known as binaural frequencies) mixed into the music.