Generate any tone, 20 Hz to 20 kHz.

440 Hz is the international tuning standard — the note A above middle C (A4), the pitch an orchestra tunes to and the reference for A = 440 in almost all modern music software. Play it here as a stable reference to tune an instrument by ear, or as the anchor for the note read-out. Some ensembles tune slightly higher (A = 442 or 443 Hz) for a brighter sound; you can dial those exactly with the ±1 Hz buttons.

528 Hz is one of the "Solfeggio frequencies" marketed as a healing or "miracle" tone said to repair DNA. There is no scientific evidence for any of those claims — physically it's just a tone about a semitone above C5, no different in nature from any other frequency. It's included as a preset because people search for it, and a 528 Hz sine is perfectly pleasant to listen to. Enjoy it as sound, not medicine.

High-frequency hearing fades with age (presbycusis) and with cumulative noise exposure. Most children hear to nearly 20 kHz; by the mid-20s many people top out around 17 kHz, and by 50 the ceiling is often 12–14 kHz. It's completely normal and usually not something you'd notice in daily life. If the tone is playing (the read-out shows it and the waveform moves) but you hear nothing at high frequencies, your speakers may also simply not reproduce that range — try the hearing test or hearing age test with headphones.

Yes, if you're careless with volume. A sustained pure tone is more dangerous than music at the same meter reading because all the energy sits at one frequency with nothing to mask it. Loud, continuous high tones can overheat and destroy tweeters; loud deep bass can bottom out a small woofer. Keep the volume moderate, don't park a loud tone at the extremes for long, and never crank a square or sawtooth wave — they carry far more energy than a sine at the same setting.

Because a square wave isn't one frequency — it's the fundamental plus a tall stack of odd harmonics (3×, 5×, 7×… the pitch). Those harmonics are what your ear reads as "buzz". A sawtooth sounds even harsher because it contains every harmonic, not just the odd ones. If you want a clean single frequency for testing or tuning, use the sine wave; the richer waves are there for timbre demos and synth-style sounds.

Small speakers physically can't move enough air to reproduce deep bass, so their output rolls off steeply below roughly 100–150 Hz. At 30 Hz you may hear faint harmonics or a mechanical buzz instead of a smooth tone — or nothing at all. That's a driver limitation, not a fault and not the generator's doing. Good headphones or a subwoofer will reproduce the low end; the bass test is built specifically for finding a system's low-frequency floor.

Play a reference pitch — 440 Hz (A4) is the usual starting point — and adjust your string or reed until the beating between your note and the tone disappears; a steady, beat-free unison means you're in tune. For other notes, change the frequency until the read-out shows the note you want with a 0-cent offset, then match it. The slow "beat" you hear as two close pitches drift in and out is the most sensitive tuning cue there is.

A steady tone holds one frequency; a sweep glides continuously from a start frequency to an end frequency over the duration you set. Sweeps are the fast way to audition a whole range at once — to find the exact frequency where a panel rattles, a room booms, or a speaker gives out. This generator sweeps logarithmically (equal time per octave), which matches how we hear pitch, so the low end isn't rushed through.

No. A pure tone is a single sine frequency; musical notes and voices are a fundamental frequency plus dozens of harmonics, plus attack and decay over time. That richness is exactly what the waveform picker demonstrates — the same 440 Hz is a clean whistle as a sine and a buzzy reed as a sawtooth. Pure tones are ideal for measurement and tuning precisely because they contain nothing but the frequency you set.