What happens is when you listen to two pure tones separated into each ear, the tiny difference causes a “frequency mismatch” as the sound travels to the auditory part of your brainstem, says Hector Orozco Perez, an author on a recent study (2022) on the mysterious beats. This frequency mismatch creates a third tone that waxes and wanes in volume— the catch is that the sound only exists in your brain. So while you hear a sort of rhythm between the two notes in binaural beats, your head is just creating a filler sound that bridges the difference between the two original sounds. For example, if your right ear is hearing 400 Hertz, and your left ear is hearing 410 Hertz, then your binaural beat comes in around 10 Hertz. What actually makes binaural beats interesting is their ability to synchronize, or entrain, your brain’s electrical response to adhere to a certain rhythm. “That’s true.” Orozco Perez says. “In auditory research, we know you can synchronize your brain with any kind of stimulus.” Our brains have certain electrical wavelengths for communicating thoughts, emotions, and so on. Tightly wound and fast-paced waves are associated with alertness and focus, while slower, more spaced-out waves are associated with relaxation and sleep.