Binaural Beat Generator

Why headphones

• The widget sends one oscillator to the left channel only and a second oscillator to the right channel only, using a Web Audio channel merger. Nothing is ever mixed into both.
• Because the two tones never meet in the air, no acoustic beat is produced. The slow throb you notice is created inside the auditory system from the difference between the two carriers — that is what makes it binaural.
• On speakers, the two tones mix before they reach your ears and you get an ordinary acoustic beat instead. Wearing only one earbud does the same thing: you hear one plain steady tone.
• Use Monitor channel → Left only and then Right only to check your headphones are the right way round and that the two pitches really are different. Solo mode releases itself after 8 seconds.

Headphone check — do this first

• Start check plays three short 660 Hz tones, each in one ear only, in a random order. After each one, press Left ear or Right ear. Replay tone repeats the current one; the three pips fill in as you answer.
• Score 3 of 3 and your channels are the right way round. Score 0 of 3 and they are almost certainly swapped — which would silently reverse every left/right reading in the widget. Anything in between is inconclusive, so run it again.
• The check has its own audio path straight to the output, so it works whether or not the tones are running, and it ducks the tones briefly so you can hear it clearly.

Perception experiment

• Binaural is the real thing: the left tone goes only to the left channel, the right tone only to the right. The two never meet, so the beat is assembled in your auditory system. It tends to feel soft, internal, and located somewhere in the middle of your head.
• Monaural sends both tones to both ears at half amplitude each. Now the two waves add and cancel in the air before they reach you, so the beat is a real, physical change in level — louder, harder-edged, and clearly out in the world rather than inside your head. Same beat rate, completely different sensation.
• Half amplitude each is deliberate: it makes the loudest instant of the monaural beat exactly as loud as the steady binaural tone. The monaural version still averages a little quieter, because it dips towards silence between beats — and that dip is the beat.
• A/B swap every 6 s alternates the two automatically so you can sit still and just listen. The button shows which one is currently sounding. Pressing either mode button by hand turns swapping off.
• Beat audibility ladder raises the beat rate through 4, 6, 8, 10, 12, 16, 20, 24, 28, 32, 36, 42, 48 and 55 Hz — past the 30 Hz ceiling of the slider, which is why it has its own control. Press Still hear it to climb, Lost it when the throb stops being a throb. There is no right answer; the point is to find your own edge.
• Then change the carrier and run the ladder again. The reported result includes the carrier you used, so you can compare 200 Hz against 1000 Hz directly.

Carrier exploration

• Carrier frequency (100–1500 Hz) sets the base pitch both ears are built around. Nudge buttons step by 1, 10 and 100 Hz.
• Sweep up 100→1500 glides the carrier across the whole range over about 24 seconds while holding the beat rate exactly where it is. Sweep down runs it the other way, Stop sweep halts it, and touching the carrier slider or its nudge buttons also cancels it.
• The sweep is exponential, so the pitch climbs at an even musical rate rather than crawling at the bottom and racing at the top.
• Listen for the beat weakening as the carrier rises. It is strongest on low carriers; most listeners find it fades somewhere around 800–1200 Hz, and by the top of the sweep it is usually gone even though the two frequencies are still exactly the same distance apart.

Session builder

• Pick a shape — Wind down 14→6 Hz, Deepen 8→2.5 Hz, Lift 6→14 Hz or Hold alpha at 10 Hz — and a length from 5 to 45 minutes, then press Start session.
• It is a scheduled ramp and nothing more: the beat rate glides in a straight line from the first value to the second over the time you chose. It does not measure you, adapt to you, or know anything about you.
• The track fills as the session runs. The labels underneath show the start and end rates with their band names, and the middle label shows the current band, the current rate, and the time remaining.
• The carrier and the sound bed stay exactly where you left them. Dragging the beat slider or pressing a band preset cancels the session, since they would be fighting each other.
• The session and the fade-out timer are independent: set the timer to the same length if you want the sound to stop when the ramp ends.

Sound bed

• Noise bed adds a decorrelated stereo wash behind the tones in three textures. Pink is the neutral reference. Rain is the same noise through a high-pass, so it hisses. Ocean is low-passed and breathes: one slow oscillator swells the level and opens the filter together on an eleven-second cycle.
• Each texture carries its own makeup gain, so switching between them does not change how loud the bed is — a filtered layer that quietly vanished would be a dead control.
• Low drone is a soft pedal on 55, 110 and 165 Hz through a gentle low-pass, on its own fader so it can sit under the tones without competing with them.
• Tones, bed and drone are all level-budgeted together: with everything at maximum the peak lands exactly at full scale, so nothing clips and no compressor is needed anywhere in the chain.

Mouse & touch

• Start tones / Stop tones fades the sound in and out over about 0.3 seconds, so there is never a click. Audio only starts on your first tap or key press, as browsers require.
• Beat frequency (0.5–30 Hz) sets the difference between the ears. The −1 −0.1 +0.1 +1 buttons nudge it a step at a time. While the ladder is running it is driven from there instead, and the slider is disabled so the two cannot disagree.
• Band presets set a sensible carrier and a beat frequency inside that band. The button for the band you are currently in stays highlighted even if you drag the sliders by hand.
• Master volume starts at a deliberately quiet 20%. Set it while the tones are playing rather than turning your system volume up.
• Fade-out timer stops playback smoothly after 3 to 30 minutes, with the remaining time counting down beside the label and in the readout strip.
• Session status beside the timer tells you which of the three automatic controls — ladder, sweep or session — currently owns the tones. Starting one cancels the others.
• Reset stops everything and restores carrier 200 Hz, beat 10 Hz, binaural, volume 20%, bed off on pink, drone off, timer off, both ears.

Keyboard

• Space start / stop · R reset · N noise bed · D low drone · B binaural / monaural · H headphone check · M cycle the monitor channel
• ← / → carrier down / up by 1 Hz · hold Shift for 10 Hz
• ↑ / ↓ beat up / down by 0.1 Hz · hold Shift for 1 Hz
• 1–5 jump to the delta, theta, alpha, beta or gamma preset
• Arrow keys are left alone whenever a slider or number field has focus, so you can step a control one notch at a time with the normal browser behaviour.
• Every button is reachable with Tab and fires on Enter or Space.

The maths

• The beat is split symmetrically around the carrier: L = carrier − beat ÷ 2 and R = carrier + beat ÷ 2, so | R − L | = beat exactly and the average pitch stays put.
• Worked example: carrier 200 Hz with a 10 Hz beat gives L = 195.00 Hz and R = 205.00 Hz. Move the carrier to 300 Hz and it becomes 295.00 / 305.00 — same beat, higher pitch.
• Changing either control while playing glides the two existing oscillators to their new frequencies. No oscillator is ever created or destroyed mid-playback — not by the sliders, not by the sweep, not by the session ramp, not by switching to monaural — which is why there is no click. Monaural switching only changes four gain values, and the sweep and the session are just fast streams of the same glide.
• The only short-lived oscillators in the widget are the headphone-check bursts, and each one stops and disconnects itself as it ends.

The bands

• δ Delta 0.5–4 Hz — commonly associated with deep sleep.
• θ Theta 4–8 Hz — commonly associated with drowsiness and meditative states.
• α Alpha 8–13 Hz — commonly associated with relaxed alertness.
• β Beta 13–30 Hz — commonly associated with active thinking.
• γ Gamma 30–100 Hz — commonly associated with high focus. The beat slider stops at 30 Hz, the bottom edge of gamma, because above that the two tones start to be heard as a rough interval rather than a beat. The audibility ladder deliberately climbs past that edge so you can hear the changeover for yourself rather than take our word for it.
• These are descriptions of frequency ranges and the states they are conventionally linked with. Evidence that listening to a matching beat reliably shifts brain activity or mood is mixed, and this widget makes no health claim.

Three things worth trying

• The honest comparison. Set 10 Hz, turn on A/B swap, close your eyes and do nothing for a minute. Most people can name which is which within two swaps — the monaural beat is out in front of you, the binaural one is inside your head. If you cannot tell them apart, that is a real and interesting result too, and worth knowing before you spend twenty minutes on a session.
• Find your own ceiling. Run the ladder at a 200 Hz carrier, note where it goes, then set the carrier to 1000 Hz and run it again. The second run is usually much shorter. Nothing in the widget asserted that to you — you measured it.
• Slow beats are the clearest demonstration. Set 2 Hz and count the throbs against a clock, then use the monitor buttons to confirm that neither channel on its own is doing anything but holding one steady tone.

Safe listening: keep the volume low — you should still hear someone talking in the room. Long sessions at moderate levels are safer than short ones at high levels. Stop if you notice ringing, discomfort or dizziness, and do not use this while driving or doing anything that needs your full attention.