Online Tone Generator: Frequency Generator 20 Hz to 20 kHz

About this tool

This online tone generator plays a pure test tone at any frequency from 20 Hz to 20,000 Hz (20 kHz) through your speakers or headphones. Type an exact frequency or drag the logarithmic slider, pick a sine, square, sawtooth or triangle wave, and use the presets for A4 440 Hz, middle C, a 1 kHz test tone or 50 and 60 Hz mains hum. A sweep mode glides between two frequencies, and a stereo test sends the tone to the left, right or both channels. Everything is generated live in your browser with the Web Audio API; nothing is downloaded or uploaded.

How to use the tone generator

1. Turn your device volume down, then press Play tone. The tone fades in over a third of a second at the page volume shown.
2. Set the frequency by typing it in hertz, dragging the slider, using the semitone and octave buttons, choosing a preset, or picking a note and octave and pressing Set note. The line under the slider names the nearest note and how many cents sharp or flat the frequency is.
3. Choose a waveform. Sine is a single pure frequency; the others add harmonics and sound brighter.
4. Test stereo with the Channel list. Left only and Right only confirm that your speakers or earbuds are the right way round; Alternate switches sides every second.
5. Run a sweep by opening Frequency sweep, entering a start, end and duration, and pressing Start sweep.
6. Press Stop when you are done. The tone also stops if you switch tabs, minimize the browser or leave the page.

How it works

Pressing Play creates an AudioContext and an OscillatorNode, the Web Audio building block that generates a periodic waveform. Its type is one of sine, square, sawtooth or triangle. The oscillator runs through a gain node for volume and then to separate left and right gains, which is how the channel test works. Stop fades the tone out and calls close() on the audio context, which MDN describes as releasing the system audio resources it uses.

The frequency slider is logarithmic, because pitch is heard in ratios: each octave doubles the frequency. Slider position p from 0 to 1 gives f = 20 × 1000^p, so the middle of the slider is about 632 Hz and every tenth of the slider is the same musical distance. The volume slider uses a square law, gain = (volume ÷ 100)², and shows the result as a peak level in dBFS, decibels relative to digital full scale: 20 × log10(gain). That level is before your device volume, so it says nothing about how loud the sound is in the room.

A logarithmic sweep uses an exponential ramp of the oscillator frequency, so it spends equal time in each octave. A linear sweep changes by the same number of hertz each second, which means it races through the low end, where octaves are only a few hertz wide.

Note frequencies and the formula

Musical notes here use twelve-tone equal temperament, where every semitone multiplies the frequency by the twelfth root of 2 (about 1.059463). The reference pitch is A4 = 440 Hz, the standard tuning frequency set by ISO 16. For a note n semitones away from A4, f = 440 × 2^(n ÷ 12). Middle C is 9 semitones below A4, so f = 440 × 2^(−9 ÷ 12) = 261.63 Hz. In MIDI numbering A4 is note 69 and middle C (C4) is note 60, so the same formula is 440 × 2^((m − 69) ÷ 12). Some software names middle C as C3 instead, so check the octave numbering if a note looks one octave off. The full chart of note frequencies from C0 to B8 is at the bottom of this page.

Waveforms and what you hear

• Sine: only the fundamental frequency. Best for tuning references and frequency checks.
• Square: the fundamental plus odd harmonics (3, 5, 7… times the frequency) at 1/3, 1/5, 1/7… of its strength. A full-scale square wave has the same RMS value as its peak, 3 dB more than a sine at the same peak, so it sounds louder and buzzier.
• Sawtooth: every harmonic, each at 1/n of the fundamental. Bright and reedy.
• Triangle: odd harmonics only, falling off as 1/n², so it sounds close to a sine with a slightly hollow edge.

Worked example

When the page loads it is set to the default tone: 440 Hz, sine wave, volume 20%, both channels. The note line reads A4, 0 cents. One cycle lasts 1000 ÷ 440 = 2.2727 ms. The volume of 20% gives a gain of 0.2² = 0.04, so the page shows -28.0 dBFS. Press + Octave and the frequency doubles to 880 Hz (A5); press + Semitone from 440 Hz instead and it becomes 440 × 1.059463 = 466.16 Hz (A♯4).

Device limits

What you hear depends on your speakers or headphones as much as on the tone. Small laptop, tablet and phone speakers often cannot reproduce low frequencies such as the 50 and 60 Hz presets, so a low sine may be faint or silent; switch to a square wave and you will mostly hear its higher harmonics. Very high frequencies may also be rolled off by headphones or by the device's audio processing. Mains hum is 60 Hz in the United States and Canada and 50 Hz in the UK and most of Europe, so pick the preset for your region when matching a hum.

Common mistakes

• Starting with the computer volume high. Turn it down first; 20% on this page is a starting point, not a safe level for every headset.
• Treating it as a hearing test. Whether a tone is audible depends on the equipment and room as well as your ears. For concerns about your hearing, see a qualified professional.
• Expecting the slider to be linear. Halfway along is about 632 Hz, not 10 kHz.

Use cases

• A 440 Hz reference for tuning instruments by ear, or any other note from the note picker.
• Checking speaker wiring and left/right channels, or finding a rattle with a slow sweep.
• A 1 kHz line-up tone for setting levels, checked with the Mic Test meter.
• Teaching sound, pitch and harmonics in a classroom, and finding a song's tempo with the BPM Finder.