Tone Generator

Generate a pure tone from 1 Hz to 20 kHz in four waveforms, with seven hearing-range presets and an exponential frequency sweep. Free and private.

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1. Tone

2. Hearing-range presets

Click a preset to set the frequency above (updates live if a tone is playing).

3. Frequency sweep

🔒 Private by design: everything runs locally in your browser and never uploaded to any server.

Written and maintained by Last updated

A single frequency, on demand

A tone generator produces one thing: a waveform at a frequency you specify, held for as long as you want it. That sounds unremarkable until you need one, at which point the alternatives are a video with an unknown frequency and compression artefacts, or software you have to install.

The uses are more varied than they look. Finding the frequency of a whine in a room by matching it. Checking the top of your own hearing range. Tuning an instrument against a reference. Exciting a room to hear where it resonates. Producing a known calibration tone for a recording chain. All of them need the frequency to be exact and adjustable while you listen.

Producing a tone

  1. Choose a Waveform. Sine is the default and is what you want for measuring anything.
  2. Set the Frequency with the slider or by typing a value in the number field.
  3. Set the Volume, starting low. High frequencies at high volume are unpleasant and inadvisable.
  4. Press play. Adjust the frequency freely while it sounds.
  5. Use a preset button to jump straight to a reference frequency.
  6. Set a start, an end and a duration in the sweep section, and play the sweep.
  7. Stop silences whichever of the two is currently running.

Waveform is not a cosmetic choice

The four waveforms sound very different and only one of them is a single frequency.

A sine wave contains its stated frequency and nothing else. If you play 8 kHz as a sine, the only energy present is at 8 kHz. That is what makes it the correct choice for any question of the form can I hear this, or does this speaker reproduce this.

A square wave, a saw and a triangle all contain the fundamental plus a series of harmonics above it, and never anything below it. They sound brighter and more present, which is exactly why they are useful for hearing whether something is playing at all, and exactly why they mislead at the bottom of the range. Play a 40 Hz square through headphones that cannot reproduce 40 Hz and you still hear its harmonics at 120 Hz, 200 Hz and upward, and conclude that the bass is there when only the harmonics are.

At the top of the range the trap works the other way round. The oscillator behind these waveforms is band limited: it generates only the harmonics that fall below half the sample rate of your audio output. On a typical 48 kHz device that ceiling is 24 kHz, and a 15 kHz square’s harmonics would sit at 45 kHz, 75 kHz and beyond, so none of them are produced at all. What you hear is the 15 kHz fundamental on its own, indistinguishable from the sine. Someone who cannot hear 15 kHz hears nothing from either, which is the honest answer rather than a false pass.

The rule survives both cases unchanged: use sine whenever the question is about one specific frequency.

Why the sweep is exponential

Pitch is perceived logarithmically. The interval from 100 Hz to 200 Hz is one octave, and so is the interval from 5 kHz to 10 kHz, even though the second spans fifty times as many hertz.

A sweep that adds a fixed number of hertz per second therefore has nothing to do with how a rise in pitch is heard. It spends most of its time inaudibly creeping through the bass and then covers the entire treble in a fraction of a second.

Ramping the frequency exponentially instead means each octave takes the same amount of time, which is the sweep that sounds like a steady continuous rise and the one that is actually useful for hearing where a system’s response changes. Set the end below the start and the same applies in reverse.

Volume, and a genuine warning

Start quiet. A pure tone at a high frequency and a high level is both very unpleasant and capable of doing real damage, and unlike music it carries none of the cues that normally make you turn something down before it hurts. This applies especially on headphones, where there is no room between the driver and your ear.

The volume control is available while a tone plays, so the safe procedure is to start near the bottom and raise it until you can just hear the tone, which is also the level at which a hearing check is meaningful.

To confirm that both speakers work and are wired to the correct sides before you trust any measurement, Speaker Test does that in a few seconds. To see the frequency content of what a microphone is picking up rather than what you are sending out, Audio Spectrum Analyzer draws the live spectrum.

For a structured check of your own hearing range rather than free exploration, Hearing Test is the right tool. For a tuning reference tied to an instrument, Guitar Tuner covers that case. For broadband sound rather than a single frequency, White Noise Generator produces the noise colours. The rest are on the audio hub.

See it in action

Screenshot of the Tone Generator tool with a tone generator with sine, square, saw and triangle waveforms, frequency and volume controls defaulting to 440 Hz at 50%, and a set of hearing-range presets that set the frequency for you
Tone Generator mid-process: a tone generator with sine, square, saw and triangle waveforms, frequency and volume controls defaulting to 440 Hz at 50%, and a set of hearing-range presets that set the frequency for you.
Diagram: where the work happens on a SysFenix page that has no file input at all: the tool arrives as ordinary JavaScript inside the page, works the answer out on your own device and renders it in place, so the upload, queue and server-side record a typical online tool needs never happen
Where the work happens on a SysFenix page that has no file input at all: the tool arrives as ordinary JavaScript inside the page, works the answer out on your own device and renders it in place, so the upload, queue and server-side record a typical online tool needs never happen.

Frequently asked questions

What frequency range and which waveforms are available?

One hertz to twenty thousand hertz, in sine, square, saw and triangle. Sine is the default and is the one to use for any measurement, since it contains a single frequency and nothing else. The other three add harmonics above the fundamental and never below it, which is what gives them their character and also what makes them the wrong choice at the low end, where an audible harmonic can pass for a fundamental you never actually heard. High up they are simply pointless, because the oscillator is band limited to half your output sample rate, so a fifteen kilohertz square has no harmonics left to add and sounds exactly like the sine.

Can I change the frequency while a tone is playing?

Yes. The slider, the number field and the preset buttons all take effect immediately on a tone that is already sounding, rather than requiring a stop and a restart. That matters for the main use of the tool, which is finding a specific pitch by ear, because stopping and starting between each attempt destroys your ability to compare one to the next.

What are the seven presets for?

They are commonly cited reference points, not a scale. Twenty hertz and twenty thousand are the conventional limits of human hearing. A hundred is low bass. Four hundred and forty is concert pitch A, the international tuning standard. A thousand is the reference tone used in a great deal of audio calibration. Eight thousand is high treble that almost everyone hears clearly. Fifteen thousand is the one most adults gradually lose with age. Clicking any of them sets the frequency field, so you can then nudge it from there.

Why does the sweep speed up as it rises?

Because it is exponential rather than linear, which is how pitch actually works. Doubling a frequency raises it by one octave whether you go from a hundred to two hundred or from five thousand to ten thousand, so a sweep that adds a constant number of hertz per second crawls through the bass and races through the treble. An exponential sweep spends equal time on each octave, which is what makes it sound like a smooth continuous rise.

How long can a sweep be?

Between half a second and sixty seconds, defaulting to five, and it runs from a start frequency to an end frequency you both choose, defaulting to two hundred up to two thousand. A sweep can go downward as well as upward by setting the end below the start. The frequency is clamped to the same one hertz to twenty kilohertz range as a fixed tone.

Why do tones fade in and out rather than starting instantly?

A waveform switched on at full volume begins partway through its cycle, and that abrupt jump is heard as a click. The volume is ramped from silence over about twenty milliseconds at the start and back down before the oscillator stops. It is fast enough to feel immediate and slow enough to remove the click entirely.

Is anything recorded, downloaded or sent anywhere?

None of those. The tone is synthesised live inside the page and sent straight to your output device, so there is no audio file at any point, nothing to download and nothing to transmit. Only one thing plays at a time, so starting a sweep stops a fixed tone and the other way round, and the stop control silences whichever is running.

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