Tone generator

From 1 Hz to 22,000 Hz. Whether you hear it is another matter: human hearing is usually given as 20 Hz to 20 kHz, and most adults stop hearing somewhere between 12 and 17 kHz. Small speakers produce little below 100 to 150 Hz, and almost no speaker reproduces the lowest few hertz — you may hear rattling or harmonics instead of the tone itself. The upper limit is also capped at half your sound card’s sample rate, which is 22.05 kHz at 44.1 kHz and 24 kHz at 48 kHz.

A sine wave is a pure tone with a single frequency. The others add harmonics — whole-number multiples of the frequency you set. Triangle adds odd harmonics that fade quickly, so it sounds soft and flute-like. Square adds strong odd harmonics and sounds hollow and buzzy. Sawtooth contains every harmonic and sounds bright, like a brass or string synth. The tool lowers the level of square and sawtooth so switching shape does not jump in loudness.

Notes use twelve-tone equal temperament: each semitone multiplies the frequency by the twelfth root of 2, and an octave doubles it. A4, the A above middle C, is the reference; the international standard sets it at 440 Hz, which makes middle C (C4) about 261.63 Hz. Some orchestras tune to 442 or 443 Hz and some music is played at 432 Hz — change the A4 reference and every note moves with it. When you type a frequency between notes, the picker shows the nearest note and how many cents (hundredths of a semitone) away it is.

The effect itself is real: play 200 Hz in one ear and 210 Hz in the other and you hear a 10 Hz wobble that exists only in your brain, which is why it needs headphones. The claims made for it are another matter. A 2023 systematic review in PLOS ONE found that of 14 studies measuring brain activity, 5 supported the idea that binaural beats entrain brainwaves, 8 contradicted it and 1 was mixed. Treat them as an interesting sound, not as a treatment for sleep, focus or anxiety.

It can if you play it loudly. Pure tones concentrate all their energy at one frequency and can seem quieter than they are, especially very high ones you can barely hear. Keep the volume low, raise it gradually, and stop if a tone is uncomfortable or your ears ring. The World Health Organization suggests keeping personal audio below 60% of maximum volume. For speakers, avoid long, loud tones at very low frequencies or at the resonance of a small driver, and keep square and sawtooth waves moderate on tweeters.

Space plays and stops. The up and down arrows move the frequency by one semitone, or an octave with Shift. The left and right arrows move it by 1 Hz, or 10 Hz with Shift. Keys 1 to 4 pick sine, square, triangle and sawtooth. Shortcuts are ignored while you are typing in a field, and the arrow keys control a slider instead when one has focus.