Tone Generator

Frequency sets the pitch, waveform sets the character, and hearing the difference between the two is the quickest way to understand timbre. A sine wave is a single frequency with nothing else in it, which is why it sounds thin and slightly eerie — almost nothing in nature produces one. A square wave at the same frequency has the same pitch but sounds hollow and buzzy, because it contains the odd harmonics stacked above the fundamental; a sawtooth contains every harmonic and sounds brighter and harsher still. That is the entire basis of subtractive synthesis, audible in about ten seconds by switching waveforms while a tone plays. If you are testing equipment, keep in mind that the limiting factor is almost always the speaker rather than the tone: the small drivers in a laptop or phone simply cannot move enough air to produce low bass, so a 50 Hz tone that sounds silent there will be clearly audible on headphones. And treat the volume seriously — a sustained pure tone carries far more energy at one frequency than music does, so it is more fatiguing and more damaging than the same apparent loudness of a song.

Musical pitch follows equal temperament from A4 at 440 Hz: the frequency of MIDI note n is 440 × 2^((n − 69) ÷ 12). One semitone is a ratio of the twelfth root of two, about 1.0595, and one cent is a hundredth of a semitone — around 5 cents is the smallest difference a trained ear reliably detects.

What you hear is limited by your speakers or headphones far more than by this tool — most laptop speakers produce almost nothing below about 200 Hz, so a 40 Hz tone may be inaudible even at full volume. Nothing here is calibrated, so it cannot measure loudness in decibels or serve as a hearing test. Browsers require a click before any audio can start, and the very top of the range is inaudible to most adults regardless of equipment.

Set 440 Hz for A4, the standard tuning reference. Doubling it to 880 Hz gives A5, exactly one octave higher; halving it to 220 Hz gives A3.

1. Set the frequency with the slider, or type an exact value in hertz.
2. Choose a waveform — sine is the pure tone.
3. Turn the volume down before pressing play, especially with headphones.
4. Press Play, then adjust the frequency while it sounds.

• Turning the volume up because a low tone seems silent, when the speaker simply cannot reproduce it.
• Treating this as a hearing test — nothing here is calibrated for loudness.
• Assuming a square and a sine wave at the same frequency are different pitches.
• Listening to sustained loud tones through headphones for long periods.

Generate a tone at any frequency between 20 Hz and 20 kHz. Choose a sine, square, triangle or sawtooth wave, watch the waveform, and see which musical note the frequency corresponds to and how many cents sharp or flat it sits.

Musicians tuning by ear, anyone testing speakers or headphones, and students learning how frequency and waveform relate to sound.

• Four waveforms, each with a live picture of its shape.
• The nearest musical note and its offset in cents, shown as you tune.
• Frequency changes smoothly while playing, with no clicks or pops.
• One-tap presets for A4, the 1 kHz reference and 60 Hz mains hum.

• Tuning an instrument against a reference pitch.
• Checking which frequencies a speaker or headphone can actually reproduce.
• Finding the frequency of a rattle or hum by matching it by ear.
• Demonstrating how waveform changes timbre at the same pitch.