40 Hz is a frequency in the brain's gamma band, the range of activity tied to attention and working memory. A 40 Hz binaural beat is one way to present that rhythm to your ears: two steady tones, forty cycles apart, one in each ear. Your brain hears the difference as a slow beat.
Quell is built on a 40 Hz binaural beat. This page is the plain version of what that means, what the research supports, and the one piece of research it is constantly confused with.
What 40 Hz is
Brain activity is grouped into bands by speed. Slow delta waves go with deep sleep; fast gamma waves go with focused thought.
| Band | Frequency | Associated state |
|---|---|---|
| Delta | 0.5 to 4 Hz | Deep sleep |
| Theta | 4 to 8 Hz | Drowsiness, meditation |
| Alpha | 8 to 13 Hz | Relaxed, calm |
| Beta | 13 to 30 Hz | Active thinking |
| Gamma | 30 to 100 Hz | Attention, working memory |
40 Hz sits low in the gamma band. Gamma activity is associated with sustained attention, working memory, and binding separate pieces of information into one thought (Jensen, Kaiser & Lachaux, 2007). Those are the mechanics of focus, which is why 40 Hz is the frequency a focus tool reaches for.
What a 40 Hz binaural beat is
Play 400 Hz in one ear and 440 Hz in the other, and you do not hear two tones. You hear one tone with a slow, 40 Hz pulse, the difference between them. That pulse is the binaural beat, and it exists in your hearing, not in the audio.
Because each ear needs its own tone, the effect requires stereo headphones. The phenomenon was popularized by Gerald Oster in Scientific American in 1973. The proposed mechanism is neural entrainment: the brain may drift toward a rhythm it is given.
40 Hz binaural beats are not the MIT gamma research
This is the confusion worth clearing up, because it is everywhere.
You may have read that 40 Hz reduces Alzheimer's pathology. Researchers at MIT drove 40 Hz gamma activity and cut amyloid plaque in mice, work now in human trials. It is real and important, and it has nothing to do with binaural beats.
That research uses physical sensory stimulation, flickering light and click-train sounds, to drive gamma directly, and it targets Alzheimer's disease. A binaural beat is a gentle auditory illusion aimed at focus. Same number, different mechanism, different goal, different evidence. Quell uses 40 Hz binaural beats for focus. It does not claim any part of the Alzheimer's work, and neither should anyone else.
What the research says about 40 Hz and focus
The evidence is genuinely mixed, and it is worth seeing both sides. One study found a working-memory benefit from a 40 Hz beat; a 2023 study of gamma binaural beats and attention found no significant effect. A broader 2019 meta-analysis found a modest overall benefit across cognitive tasks. The fair reading is that 40 Hz may help attention a little for some people, and the studies are small and not unanimous. We lay this out in full on the science page.
How Quell uses 40 Hz
Quell generates the two tones on your device and sends one to each ear, so the beat is created in your hearing in real time with nothing to stream. It centers the beat on a low, warm carrier rather than a bright one, which makes a long session easier to sit with. The 40 Hz beat is the free, default layer; an optional coach voice and focus music sit on top, and the timer counts up so nothing rushes you.
Try it against the practical guide to binaural beats for focus, or see how it applies to an ADHD brain.
Quell is a focus tool, not a medical device. It is not intended to diagnose, treat, cure, or prevent any condition.