How binaural beats work
The mechanism is simple, well understood, and much less mysterious than most pages about it. Here it is, including what this generator does with the numbers you set.
Play two tones of slightly different frequency, one into each ear, and neither ear hears a beat — but the auditory system, comparing the two signals, produces the perception of a slow throb at the difference frequency. 200 Hz left and 204 Hz right gives a 4 Hz binaural beat. The beat exists in perception, not in the air.
Why headphones are not optional
If both tones reach both ears — from speakers, say — they interfere physically before they arrive, and you hear an ordinary acoustic beat: the same throb, but produced in the room rather than in your head. It is a different phenomenon with a different feel, and it is why a binaural file played on a speaker is not doing what the label says.
The separation also has to be real. A mono Bluetooth profile, a single earbud, or a phone summing both channels all destroy it. That is what the headphone test is for.
Carrier and beat: two different numbers
| Carrier frequency | Beat frequency | |
|---|---|---|
| What it is | The pitch you actually hear | The difference between the ears |
| Typical range here | 100–500 Hz | 0.5–40 Hz |
| If you change it | The tone gets higher or lower | The throb gets faster or slower |
| Audible on its own | Yes | No — 4 Hz is below hearing |
| What most pages mean by “frequency” | Rarely this | Usually this |
The confusion between these two numbers is behind a great deal of nonsense online. A “10 Hz track” does not contain a 10 Hz tone — 10 Hz is far below the range of human hearing and no headphone reproduces it. It contains two audible tones 10 Hz apart.
What the beat frequency is named after
The band names — delta, theta, alpha, beta, gamma — come from EEG, where they describe rhythms measured at the scalp. Borrowing them for audio is a naming convention with a hypothesis attached: that a sound pulsing at a rate might nudge brain rhythms towards it, which is called entrainment. Whether audio entrainment happens reliably, and whether it produces effects anyone would notice, is precisely the part that is not settled.
What this generator actually does
- Two sine oscillators, one routed to each channel. The right is set to carrier + beat in binaural mode, or to the carrier in every other mode.
- For isochronic mode, a low-frequency oscillator modulates the amplitude of a single tone at about 42% depth — audible pulsing, no clicks.
- The noise bed is generated from a random source: white raw, pink through a filter cascade, brown by integration, green by band-passing pink.
- Everything is synthesised live in your browser with the Web Audio API. There are no audio files on this site, which is why nothing has to load before it plays.
- The timer counts on the audio clock rather than a page timer, so a backgrounded tab still fades out on schedule.
Sample rate is whatever your device runs at — usually 44.1 or 48 kHz. Everything is computed in 32-bit float and rendered stereo.
Do the presets mean anything?
They are starting points chosen from convention, not prescriptions. “Delta 2 Hz” means the beat is 2 Hz and the carrier is low; it does not mean the sound will put you into delta sleep. We name them after the bands because that is what people search for, and we would rather label them honestly than invent proprietary names for the same numbers.
Questions
What is the difference between carrier and beat frequency?
The carrier is the pitch you hear; the beat is the difference between the two ears. A 200 Hz carrier with a 4 Hz beat means 200 Hz in one ear and 204 Hz in the other.
Why can I not hear a 4 Hz tone?
Human hearing starts around 20 Hz. A 4 Hz binaural beat is a perceived modulation of two audible tones, not a 4 Hz sound.
Does the carrier frequency matter?
For how it feels, yes — beats are easiest to perceive with carriers roughly between 100 and 500 Hz. For any claimed effect, there is no evidence that one carrier beats another.
Is entrainment proven?
Frequency-following responses to rhythmic sound can be measured in some conditions. Whether that produces reliable effects on sleep, mood or attention is a separate and much less settled question.