Binaural beats
Play a steady tone in one ear and a slightly different one in the other, at the same time, through headphones. Most listeners hear a slow pulsing at the difference between the two. 400 Hz on one side and 420 Hz on the other gives a 20 Hz beat, and it seems to sit inside the head.
That pulse is the binaural beat.
It is not in the recording
The beat is not in the air and not in either ear. Your brain constructs it by comparing the two signals.
The long-standing account is that the comparison begins at the first point in the hearing pathway that receives from both ears. People who work on this still write “thought to originate” there, which is the right level of confidence. In humans, responses to the beat turn up much further along, all the way to the auditory cortex.
What it actually feels like
Nothing at the beat frequency exists in the sound. What changes is where the fused tone seems to sit, and how loud it seems, as the two drift in and out of step with each other.
- Below about 3 Hz, it feels like a sound rotating between your ears.
- Up to about 20 Hz, it is a smooth pulse in loudness.
- Above that it turns rough.
- Past roughly 30 Hz it gives up and breaks into two separate tones.
Those boundaries are approximate and they vary between people.
The tones have to overlap
This is the part that matters most, and it is where most confusion in this subject comes from.
The two tones have to play together, continuously. If they take turns, there is no binaural beat at all. You just hear two tones alternating.
This is not a matter of degree. Alternation does not weaken the effect. It removes it.
Headphones are not optional
Each ear has to hear only its own tone. Headphones or earbuds are the only ordinary way to guarantee that.
Through speakers, both tones reach both ears and interfere in the air. You do hear a real throbbing, and it is often more obvious than a binaural beat, which is exactly why people conclude that speakers work fine. It is a different effect, made at your ear rather than in your brain.
The useful range
Binaural beats are a low-frequency thing. Around 1000 Hz they do not so much stop as become hard work. Lower tones give a more vivid beat, and the region around 400 Hz gives the widest range of usable beat rates.
The difference between the two tones has to stay under roughly 30 Hz or you start hearing two separate tones instead, and that ceiling narrows as the tones themselves go higher.
Set the volume so the tones are clearly and comfortably audible, then leave it. Louder does not strengthen the beat. Too quiet does weaken it.
Does it work
There is modest evidence that binaural beats help with situational anxiety. The effects reported are small and they are not consistent from study to study.
Not everyone hears the beat at all. One classic estimate put it at about half of listeners, though other work implies nearly everyone does.
You can hear one of these next to the other, which settles the distinction faster than any description.
If you want the evidence itself, it is all here.