Binaural Beats — Sleep & Focus

Binaural beats are an auditory illusion: when each ear receives a steady tone at a slightly different frequency, the listener hears a third, pulsing tone at the difference between them. This generator synthesises two isolated sines with the Web Audio API, pans them hard left and right, and offers optional masking noise. Audio never leaves the browser.

How to use it

1. Put on stereo headphones. The page shows a headphone notice because the two tones must stay separated until they reach your ears; loudspeakers mix them in the air first.
2. Choose a band card. Delta (0.5 to 4 Hz), Theta (4 to 8 Hz), Alpha (8 to 13 Hz), Beta (13 to 30 Hz) and Gamma (30 to 50 Hz). Each card sets the beat slider to its preset.
3. Set the carrier. The carrier slider runs from 100 to 500 Hz in 5 Hz steps and defaults to 200 Hz. The readout shows the split: a 200 Hz carrier with a 10 Hz beat gives 195.0 Hz left and 205.0 Hz right.
4. Fine-tune the beat. The beat slider spans 0.5 to 45 Hz in 0.5 Hz steps, and the matching band card highlights as the value crosses a boundary.
5. Set the tone volume. The slider runs from 0 to 90 percent and defaults to 40 percent; starts and stops fade over 50 ms.
6. Add masking noise if the room is noisy. Choose None, Pink or Brown Noise, with its own slider from 0 to 50 percent.

The beat is the difference frequency

The beat rate is the absolute difference between the two tones: f_beat = |f2 - f1|; the carriers sit symmetrically around the selected value at carrier plus or minus half the offset.

A 200 Hz carrier with a 10 Hz beat produces 195.0 Hz in one ear and 205.0 Hz in the other, and the percept is a 10 Hz pulsation. Three practical limits appear in the literature: carriers below about 1000 Hz, offsets under roughly 30 Hz before a pulse turns into roughness, and strongest perception with carriers near 400 Hz. All three sit inside this generator’s 100 to 500 Hz range and 45 Hz maximum offset.

Each ear receives a steady sine, so neither channel beats on its own. The interaction happens in the auditory brainstem, where the superior olivary complex, the first stage to receive input from both ears, compares phase. That comparison produces the slow loudness pulsation, heard inside the head rather than at a speaker.

The headphone rule follows from that mechanism. Summed to mono, each ear gets both frequencies and they interfere at the eardrum, producing an ordinary monaural beat at the same |f2 - f1| rate. A monaural beat is real and often stronger, but it is not binaural: the binaural component depends on separate delivery to each ear. Speakers can never reproduce it, and a mono listening mode turns this page into a monaural beat generator.

Bands, carriers and what the evidence supports

The five band names come from EEG research, and the step from a beat rate to a mental state is where the caveats start.

Band	Beat range	Preset	Evidence for brainwave entrainment
Delta	0.5 to 4 Hz	2.5 Hz	Not established
Theta	4 to 8 Hz	6 Hz	Inconsistent across studies
Alpha	8 to 13 Hz	10 Hz	Some small effects reported
Beta	13 to 30 Hz	18 Hz	Weak and inconsistent
Gamma	30 to 50 Hz	40 Hz	Mixed results

The labels assume brainwave entrainment: that stimulation at a given rate makes cortical oscillations follow. The auditory system does produce phase-locked responses to rhythmic sound, including the frequency-following response, so the mechanism is plausible. Evidence is weaker than the marketing. Ingendoh et al. (2023) reviewed 14 EEG studies and found five consistent with entrainment, eight with no effect and one mixed, with wide differences in method. Meta-analyses of behavioural outcomes report small average effects on anxiety and cognition, with substantial variation between studies. What is established is the beat percept; what is not is that listening changes your mental state on demand. Treat the band names as labels for beat rates.

For practical use, pick a rate you find pleasant, keep the level low, and allow ten to fifteen minutes; masking noise helps in a noisy room. If you have epilepsy or a seizure history, the on-page notice asks you to consult a physician first, and nobody should listen while driving.

Accuracy, limits and troubleshooting

• Headphones must provide real channel separation: a mono accessibility setting, a mono Bluetooth route or a spatial-audio downmix collapses the channels into a monaural beat.
• Both tones come from one audio graph panned fully left and right, so the channels are inherently in sync; Bluetooth latency shifts the pair together without changing the beat rate.
• Carriers above roughly 1 kHz stop producing a clear binaural percept, and offsets above roughly 30 Hz sound rough rather than pulsing; both sit outside this tool’s controls.
• Perception varies widely: some listeners hear only two steady tones. Beats below about 3 Hz feel like a slow swell rather than a pulse, while high rates blur into roughness.
• The volume sliders set digital gain, not dB SPL. Set level by comfort, keep sessions short, and do not fall asleep with headphones at a high level.
• This is a relaxation and acoustics demo, not a medical device. It does not treat sleep, anxiety or pain, and it cannot diagnose anything; if a health concern is behind your interest, speak to a clinician.
• The tones are pure sines with no harmonics, so any buzz comes from EQ or enhancement processing later in the chain.

Related tools

• Tone Generator — compare one steady sine against the binaural pair at the same carrier frequency.
• Headphone Test — verify channel separation and driver matching before trusting a binaural listen.
• Noise Generator — audition pink and brown masking noise on their own.