Online tone generator

A continuous test tone at any frequency from 20 Hz to 20 kHz, in four waveforms, with the level set in dBFS. Changes apply while the tone is playing.

Protect your hearing and your speakers. Turn your device volume down before you press play, then bring it up slowly. Pure tones are fatiguing, high frequencies can be loud even when they are hard to hear, and sustained high-level tones can damage tweeters. Headphones need extra care.

Tone

440 Hz

Nearest note A4 (+0.0 cents at A4 = 440 Hz). One cycle lasts 2.273 ms, and the wavelength in air at 20 °C is 78.0 cm.

Sweep

From (Hz)

To (Hz)

Duration (s)

Exponential: 6.6 octaves in 20 s, 0.33 octaves per second.

Harmonics in the square wave at 440 Hz

The ideal Fourier series, up to 20 kHz. A sine has only its fundamental, so this table shows the square wave until you pick another shape.

Harmonic	Frequency	Amplitude	Level vs fundamental
1 (fundamental)	440 Hz	1.000	0.0 dB
3	1320 Hz	0.333	-9.5 dB
5	2200 Hz	0.200	-14.0 dB
7	3080 Hz	0.143	-16.9 dB
9	3960 Hz	0.111	-19.1 dB
11	4840 Hz	0.091	-20.8 dB
13	5720 Hz	0.077	-22.3 dB
15	6600 Hz	0.067	-23.5 dB

How to use it

Choose a waveform, type a frequency or drag the slider, and press Play tone. The slider is logarithmic, so each octave takes the same distance: the middle of its travel is about 632 Hz, not 10 kHz, which matches how pitch is heard. The octave and semitone buttons multiply the frequency by 2, ½ or 2^±1/12 (about 1.0595), so you can step through equal-tempered notes from any starting point.

The level control sets the digital amplitude in dBFS, decibels relative to full scale. At −20 dBFS the peak of a sine wave is one tenth of the largest value the audio output can represent. Your device volume and amplifier then decide how loud that is in the room; this page cannot know or control that. Tones start and stop with a short fade so they do not click.

What each waveform is for

Sine: a single frequency with no harmonics. Use it for tuning references, checking speaker and room response one frequency at a time, rough checks of your own upper hearing limit (not a medical hearing test), and finding rattles and buzzes in cars, cabinets and rooms.
Square: odd harmonics (3rd, 5th, 7th…) falling at 1/n, so the 3rd harmonic is 9.5 dB below the fundamental. Bright, hollow and much louder-sounding than a sine at the same peak level.
Sawtooth: every harmonic at 1/n. The brightest of the four and the classic starting point for subtractive synthesis.
Triangle: odd harmonics falling at 1/n², so the 3rd is already 19.1 dB down. It sounds close to a sine with a little edge.

The maths behind the readout

The nearest note uses twelve-tone equal temperament with A4 = 440 Hz: the note number is 69 + 12 × log2(f / 440), rounded, and the offset in cents is 1200 × log2(f / f_note). The period is 1000 / f milliseconds. The wavelength is c / f with the speed of sound c taken as 343 m/s, its value in dry air at 20 °C. It rises by roughly 0.6 m/s per degree, so wavelengths in a cold room are slightly shorter.

Worked example. 440 Hz is exactly A4, 0 cents. One cycle lasts 1000 / 440 = 2.273 ms and one wavelength is 343 / 440 = 0.78 m. Press ×2 and you get 880 Hz, A5, with a wavelength of 39 cm. Press +1 semitone from 440 Hz and you get 466.16 Hz, A#4.

The sweep is exponential: the frequency at time t is f1 × (f2 / f1)^t/T, so it spends equal time in every octave. A linear sweep would race through the bass, where most room and speaker problems are, and dawdle in the treble. A 20 Hz to 2 kHz sweep covers log2(100) ≈ 6.6 octaves.

Where it stops being reliable

The tone is generated correctly, but what reaches your ears depends on the chain after the browser. Small speakers cannot reproduce deep bass at all, and some phones and laptops apply their own equalisation and limiting, which can add harmonics or change the level as you sweep. Bluetooth headphones compress the signal and add latency. For measuring equipment, use a wired output and turn off any "enhancement" settings in the operating system.

This page does not measure anything: it only plays sound and does not use your microphone. A sweep helps you hear resonances and rattles; a measurement microphone and analysis software are what you need to put numbers on them. The room mode calculator predicts where the strongest bass resonances in a rectangular room should fall, which gives you frequencies to try here.

Common questions

5 answers

Why can I not hear the tone at very low or very high frequencies?

Usually the playback equipment, not your ears. Laptop and phone speakers produce very little below about 150–200 Hz, and many earbuds roll off below 40 Hz. At the top end, hearing above 15 kHz declines with age and noise exposure, so a 17 kHz tone that a teenager hears clearly may be silent to an adult. Be careful turning the volume up to compensate: the tone may be playing at a high level even when you cannot hear it.

Is the frequency exact?

It is as exact as your device’s audio clock. The Web Audio API generates the waveform digitally at your output sample rate (normally 44.1 or 48 kHz), and sound-card clocks are typically accurate to a few tens of parts per million, which at 440 Hz is a small fraction of a cent. That is far better than any ear, and good enough for tuning, but it is not a calibrated laboratory reference.

What level in dBFS should I use?

Start low. The default of −20 dBFS leaves 20 dB of headroom and is a common alignment level for test tones. Set the tone first, then raise your system volume slowly. Square and sawtooth waves sound much louder than a sine at the same dBFS setting because they carry energy in many harmonics, so reduce the level when you switch to them.

Can I use this to find out what frequency my tinnitus is?

Some people use tone generators to describe the pitch they hear to a clinician, but this page is not a medical tool and cannot diagnose or treat anything. If you have tinnitus, see an audiologist or doctor, and keep test tones quiet: loud sound is one of the things that makes it worse.

Why does the square wave not look perfectly square on a scope?

Because a perfect square wave needs infinitely many harmonics and the digital output cannot contain anything above half the sample rate. The browser builds its square, sawtooth and triangle waves from a band-limited set of harmonics to avoid aliasing, so you will see some ripple (the Gibbs effect) near the edges. Your sound card’s output filter shapes it further.

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