Tone Generator

What a tone generator is for. It plays one frequency, steadily, for as long as you want it. That sounds trivial and it is exactly what makes it useful: a pure tone is a signal with nothing else in it, so anything you hear that is not the tone is coming from your equipment, your room or your ears. Sweep it slowly and a rattle in a speaker cabinet shows up at one specific frequency and nowhere else. Play it in one channel and a wire that is not connected becomes obvious in a second.

Tuning by ear. Pick a note from the list and the frequency snaps to it exactly — A4 is 440 Hz, the guitar's low E is 82.4 Hz, a bass low E is 41.2 Hz. Play it, hum or pluck along, and listen for beating: when two pitches are close but not equal you hear a slow wobble, and the further apart they are the faster it wobbles. Tune until the wobble slows down and stops. This is how instruments were tuned for centuries and it is more precise than most people expect — a trained ear resolves a couple of cents this way, which is better than reading a needle.

Testing speakers and headphones. Start around 100 Hz at a modest level and walk the slider slowly upward. What you are listening for is anything that changes character: a buzz that appears and disappears over a narrow range is usually something loose in the cabinet or the room rather than the driver. Below about 60 Hz most laptop and phone speakers produce almost nothing, which is not a fault — the driver is too small to move enough air. Above 15 kHz many adults hear nothing at all, and that is also not a fault.

Finding where your hearing stops. Set a comfortable level around 1 kHz, then raise the frequency without touching the level. The point where the tone disappears is a rough upper limit for your hearing. Expect somewhere between 17 kHz and 20 kHz in your teens, and for that number to fall by roughly a kilohertz a decade after that. Treat it as a curiosity rather than a test: what you actually measure is a combination of your ears, your speakers, your volume setting and the noise in the room, and only one of those is your hearing. A real audiogram is done in a quiet booth with calibrated headphones.

What the four waveforms are. A sine is one frequency and nothing else, which makes it the reference for everything above. The other three add harmonics — whole multiples of the frequency you set — and that is what makes them sound brighter without sounding higher. A triangle has odd harmonics that fall away quickly, so it is soft. A square has odd harmonics that fall away slowly, giving it a hollow, clarinet-like edge. A sawtooth has every harmonic and is the brightest and loudest-sounding of the four at the same level. For testing equipment, use the sine: with anything else you cannot tell whether what you are hearing is the speaker misbehaving or a harmonic that was in the signal all along.

Please be careful with the level. A steady tone is genuinely more dangerous than music at the same setting, in two directions. It is far more tiring and damaging to your ears, because there are no quiet moments in it and no variety for your hearing to rest against — and sustained exposure above about 85 dB is what causes permanent hearing loss. It is also hard on tweeters, which are built on the assumption that high-frequency content arrives in short bursts. This tool starts at a low level for that reason. Turn your system volume down before pressing Play and bring it up from there, and be especially careful above 2 kHz in headphones, where a tone that reads as unremarkable on a laptop speaker is painful.

How it works, and what it does not do. The tone is synthesised in your browser with the Web Audio API — a single oscillator through a gain and a stereo panner — so there is no audio file to download and the tool works with the network switched off. It fades in and out over about 20 milliseconds rather than starting instantly, because a waveform that jumps from silence to full amplitude is a step, and a step is a click that can be louder than the tone. Nothing is recorded and nothing is uploaded; the waveform, frequency, channel and level are stored in this browser, and the link in the address bar is the only thing that leaves the page.