Isochronic Tone Generator

Listen safely. Volume starts at 20 % on purpose. Turn your system volume down before pressing Play, then raise it slowly. A repeating tone is fatiguing; keep sessions moderate and take breaks. Do not use this while driving or operating machinery, and stop if it becomes uncomfortable. This applies to every mode here, including the sequencer, the session ramp and the listening game.

Photosensitivity. Nothing here flashes the screen. The sequencer’s moving step highlight is a soft outline, it is switched off automatically above 12 Hz, and it never runs when your system asks for reduced motion — a step number is shown as text instead. The drawings are line graphics, not strobes. If you have epilepsy, a seizure disorder or any medical concern, talk to a clinician before using pulsing audio or pulsing visuals.

What an isochronic tone is

A single carrier tone is gated on and off at a regular rate — for example 10 times a second. The pulsing is physically present in the sound wave itself, so it works on a laptop speaker, a phone or one earbud. A binaural beat is different: it plays two slightly different frequencies, one in each ear, and the "beat" only appears if you wear headphones so the ears stay separated. Isochronic tones need no headphones; binaural beats do.

Duty cycle

Duty cycle is the share of each cycle in which the tone is on. At a 100 ms period, 50 % duty is 50 ms on and 50 ms off; 20 % duty is 20 ms on and 80 ms off. Low duty gives short, dry ticks with lots of silence. High duty gives a nearly continuous tone with a shallow throb. The formulas used here are period = 1 / rate, on = duty × period, off = (1 − duty) × period.

Why the ramp matters

A hard square gate jumps the amplitude from 0 to full instantly. That step contains a burst of broadband energy and you hear it as a click on every pulse. Giving the edges a short attack and release — a few milliseconds is enough — removes the click and leaves a clean pulse. Use the Hard gate / Smooth ramp A/B buttons while the tone is playing to hear the difference, and watch the corners of the drawn gate square off or round over. At fast rates with a low duty cycle the on-time is very short, so the ramp is automatically limited to fit inside it; the widget tells you when that happens.

Hz and BPM are the same number

A pulse rate is a tempo. One pulse per second is 60 beats per minute, so BPM = Hz × 60 and Hz = BPM ÷ 60. That makes 10 Hz exactly 600 BPM, 2 Hz exactly 120 BPM, and 0.5 Hz exactly 30 BPM. Both numbers are shown at all times and either field drives the other; the widget’s 0.5–40 Hz span is 30–2400 BPM. Tap tempo lets you tap a pulse in with the mouse, the keyboard or a finger: it averages your last taps and sets the rate. If you are thinking in musical terms, remember that a 600 BPM pulse is the same thing as 150 BPM in sixteenth notes.

Accent and grouping

Set grouping to 2, 3, 4, 6 or 8 and the first pulse of every group is played at full level while the rest are pulled down by the accent depth. The timing does not change at all — every pulse still lands exactly on the grid — only the peak gain of the scheduled gate changes, so 12 Hz in groups of 3 reads as a fast waltz rather than a flat stream. The drawing shows the taller accented pulses and a dashed line marking the unaccented level.

Pattern sequencer

Switch the sequencer on and the pulse train stops being uniform: a pattern of 8, 12 or 16 steps loops at the chosen rate, and each step is one pulse period. Tap a step to cycle it through three states — off (silent, the gap simply continues), on (unaccented) and accent (full level). The written pattern is shown underneath in the form X.X.XX.., where X is an accent, x is a normal pulse and . is a rest.

Nothing about the timing loosens when the sequencer runs. Each step is still scheduled on the audio clock by the same lookahead scheduler, so a 16-step pattern at 10 Hz repeats every 1.6000 s indefinitely without drifting. A rest is not a shortened cycle; it is a cycle in which the gate is simply never opened. The preset buttons fill the grid with a few starting points, including the X.X.XX.. from the label and a random fill.

Session ramp

The ramp schedules the pulse rate to glide from one value to another over a chosen number of minutes — for instance 20 Hz down to 6 Hz over 10 minutes — and draws a progress track while it runs. The glide is logarithmic, so equal stretches of time cover equal musical ratios and the movement sounds even rather than rushing at one end.

Be clear about what this is. It is a scheduled frequency ramp and nothing more: at every moment the widget works out the rate from the elapsed audio time and schedules the next pulse at that rate. It is not a programme, a protocol or a treatment, and no effect on the listener is claimed or implied. Moving your controls by hand cancels the ramp.

Listening game

How fast is it? plays a mystery pulse rate and offers four answers in Hz and BPM. Getting one right raises your score and your streak; getting one wrong resets the streak and shows the true rate. It is a decent ear trainer: most people are much better at ranking rates than at naming them.

Flutter → tone is the interesting one. It ramps the pulse rate upward from around 4 Hz and you press the button at the moment you stop hearing separate events and start hearing one rough, buzzy pitch. Somewhere in the region of roughly 15–25 Hz a rhythm turns into a timbre: the individual pulses fuse, the repetition rate becomes a perceived low pitch, and what was tempo becomes tone colour. Where exactly that happens depends on you, on the duty cycle, on the carrier and on your speakers, so there is no single correct number and the game does not score you — it just reports where you pressed. It is a listening curiosity, not a test of anything.

Second carrier and noise

The carrier does not have to be one bare sine. Add a second carrier at a musical interval above the first — minor third, major third, fourth, fifth or octave — and both tones are gated by the same envelope, so the rhythm is identical while the texture becomes a chord. The interval tracks the carrier: move the carrier and the second voice follows it. The noise blend crossfades the carrier towards white or pink noise; at 100 % the pulsing is carried entirely by noise, which sounds like a soft shaker or a rhythmic wash and removes pitch from the equation completely. Pink noise has less high-frequency energy than white and is easier on the ears.

Mouse

• Pulse rate slider — drag to sweep 0.5–40 Hz. The scale is logarithmic so the slow end stays controllable. The readout shows rate in Hz and the period in ms.
• BPM field — the same rate in beats per minute, 30–2400. Type a tempo and press Enter, or nudge by ±1 and ±10 BPM. Tap tempo averages your taps; Clear taps starts the averaging again.
• Grouping — Off, 2, 3, 4, 6 or 8 pulses per accented group. Accent depth sets how much quieter the unaccented pulses are.
• Sequencer — the on/off button arms it, 8 / 12 / 16 sets the pattern length, and each step button cycles rest → pulse → accent. Presets fill the grid; Shift-clicking a step clears it straight back to a rest.
• Session ramp — type a From and To rate in Hz, choose a length in minutes, press Start ramp. The track fills as it runs and the caption shows the live rate; the preset buttons load common band-to-band moves.
• Listening game — pick a mode, press the big button, then answer. Score, current streak and best streak are kept for the session only, in memory, and are lost when the page is closed.
• Second carrier — Off, m3, M3, P4, P5 or 8ve above the carrier. Noise blend mixes the carrier towards noise; White / Pink choose the colour.
• Rate field — type an exact rate and press Enter. −1 / −0.1 / +0.1 / +1 Hz are fine nudges.
• Duty cycle — 10–90 %. Changes the sound and the drawn envelope immediately.
• Attack / release — 2–50 ms edge smoothing. Disabled while Hard gate is selected, because a hard gate has no ramp.
• Gate shape — Hard gate (instant, clicks) versus Smooth ramp. Auto A/B alternates between them every two seconds so you can compare hands-free.
• Carrier — 100–1000 Hz slider plus an exact field and ±1 / ±10 Hz nudges. Four waveforms: sine, triangle, square, sawtooth. Sine is the least harsh.
• Bands — each button sets the pulse rate to a value inside that band. The band containing the current rate is outlined even if you set the rate by hand.
• Volume — 0–60 %. Fade timer — pick a duration; the countdown runs while playing and the last 8 seconds fade out smoothly before the tone stops.
• Reset — returns every control to its default and stops the tone.

Touch

• Drag any slider thumb; every button is at least 40 px tall and every grid — including the 16-step sequencer — is fully visible and wraps rather than scrolling.
• Tap a band or waveform button to select it; the selected one fills with the accent colour.
• Tap a sequencer step repeatedly to cycle rest → pulse → accent. Tap Tap tempo in time with a beat to set the rate by feel.

Keyboard

• Space start / stop.
• ← → pulse rate −/+ 0.5 Hz (hold Shift for 0.1 Hz).
• ↑ ↓ duty cycle +/− 5 % (hold Shift for 1 %).
• [ ] carrier −/+ 10 Hz  ·  , . ramp −/+ 2 ms.
• 1–4 waveform  ·  5–9 Delta, Theta, Alpha, Beta, Gamma.
• G toggle hard / smooth gate  ·  R reset.
• S sequencer on / off  ·  A cycle the accent grouping  ·  T tap tempo.
• Shortcuts are ignored while a slider or a number field has focus, so native slider and typing behaviour still work. Click the widget background first.

About the band names

Delta, Theta, Alpha, Beta and Gamma are simply the conventional frequency ranges electroencephalography uses to describe brain activity: Delta 0.5–4 Hz, Theta 4–8 Hz, Alpha 8–13 Hz, Beta 13–30 Hz, Gamma 30–100 Hz. Here they are only shortcuts for setting the pulse rate. The evidence on whether listening to a pulsing tone shifts brain rhythms, mood, focus or sleep is mixed and far from settled — studies are small, results are inconsistent, and this widget makes no health, therapeutic or medical claim of any kind. Treat it as a sound tool, not a treatment. Anyone with epilepsy, a seizure disorder or any medical concern should talk to a clinician before using audio like this.

The same applies without exception to every mode added here. The session ramp is a scheduled frequency glide, the sequencer is a rhythm pattern, the grouping control is a gain accent and the game is a listening exercise. None of them is a protocol, a programme or a treatment, and no health, therapeutic or medical benefit is claimed for any of them.

Tips

• Find where rhythm becomes pitch. Open the listening game, choose Flutter → tone and press start. Listen for the moment the ticking fuses into one buzzing note. Then set the rate by hand a couple of Hz either side of your answer and switch back and forth — the boundary is surprisingly sharp once you know where it is, and it moves if you change the duty cycle.
• Make it musical. Set 8 Hz (480 BPM), turn the sequencer on at 16 steps and load the X.X.XX.. preset. Add a fifth on the second carrier, push the noise blend to about 35 % and drop the duty to 20 %. That is a usable percussive pattern, not a wellness demo — and it is still the same gate scheduled on the same clock.
• Watch a ramp cross a band edge. Load the 20 Hz → 6 Hz preset over 5 minutes and leave the band buttons in view: the outline moves from Beta to Alpha to Theta as the rate passes 13 and 8 Hz. The bands are just labels on a number line, and seeing the ramp cross them makes that obvious.
• Hear the click, then kill it. Set rate 10 Hz, duty 50 %, carrier 200 Hz, press Play, then hit Auto A/B. The hard gate ticks on every edge; the smooth ramp does not. Then drop the ramp to 2 ms and back up to 30 ms to hear how soft the pulse can get.
• Duty cycle is the character control. Keep the rate fixed and sweep duty from 15 % to 85 %: the same 10 Hz goes from a dry stutter to a gentle tremolo without the tempo changing at all. Watch the ON and OFF numbers track it.