Tone Generator

It's there when the house goes quiet: a faint buzz from somewhere near the desk, too vague to locate by pointing your ear at things. You've checked the fridge, the router, the ceiling fan. The sound doesn't care — it persists, politely, at the edge of perception, and it's loudest at 11 p.m. when everything else stops competing.

This is the moment a tone generator becomes a surprisingly domestic instrument. Sweep the frequency range and the buzz will announce itself at one specific spot on the dial — the tone and the mystery sound lock together, suddenly obvious. Now you're not hunting a sound; you're hunting a thing that resonates at, say, 120 Hz, which in North America points at anything with a small transformer on the mains. One aging USB power brick gets unplugged, and the bedroom is quiet for the first time in weeks.

Hums are only the beginning. The same dial is a speaker tester, a hearing check, a physics demonstration, a tinnitus masker, a tuning reference, and a way to find which of your studio monitors is lying to you. It runs on pure mathematics inside your browser — no downloads, no uploads, no reason to trust anyone's server with anything. Press play and the sine wave simply exists.

1. 1

   Dial a frequency

   Type a value or drag the slider anywhere from 1 Hz to 22,000 Hz. The readout shows the note name too — 440 Hz, for instance, is A4, the note orchestras tune to.

2. 2

   Pick a waveform

   Sine for pure measurement, square, sawtooth, or triangle when you want harmonics in the picture — or white/pink noise when you want all frequencies at once.

3. 3

   Set the level

   Start low. A continuous tone at comfortable music volume is more fatiguing than music; bring it up only as far as the job needs.

4. 4

   Play, sweep, or render

   Hold a steady tone for testing, run a logarithmic sweep between two frequencies to hunt resonances, engage dual-tone mode for beats, or render a stretch of audio to a file for use in edits and ringtones.

A pure tone is pressure oscillating smoothly back and forth at one fixed rate — the mathematical sine wave. Frequency counts the oscillations per second in hertz: 440 Hz means the air (and your speaker cone) swings 440 times each second, and you hear the single, steady pitch that orchestras agree to call A. Doubling the frequency raises the pitch by one octave — 440 to 880 — which is the geometry of every scale ever written.

The browser makes these tones the direct way: it computes them. The Web Audio API's OscillatorNode is an oscillator in the literal engineering sense — a running phase accumulator that generates each output sample as the sine of the phase, in real time, from your device's audio clock. There is no audio file being stretched, no sample being pitched up; 137 Hz exists because the math said 137 Hz, sample by sample, for as long as you hold the button.

That origin matters for what the tool is honest about. A synthesized sine at a dialed frequency is that frequency — within the tolerance of the crystal clock, which is far tighter than any ear or speaker in the chain. What it is not is calibrated loudness: the level you hear depends on your volume slider, your speakers, and your distance from them. Frequency is absolute on this page; loudness is your responsibility.

Why does a violin and a flute playing the same note sound different? Overtones — integer multiples of the fundamental frequency, each at its own amplitude. Every sustained sound is a stack of these harmonics, and the stack's shape is the timbre. The generator's waveform buttons are that principle made playable: each shape is a fixed, famous recipe of harmonics, and hearing them side by side is the fastest music-theory lesson a browser can give.

The two workhorse recipes for the curious: a square wave is a sine plus a third of the third harmonic plus a fifth of the fifth, onward forever; a sawtooth is every harmonic at the inverse of its number. Fourier's insight — that any repeating wave decomposes into sine sums exactly like these — is the mathematical backbone of every codec, equalizer, and synthesizer you've ever used. This page is Fourier's theorem with a volume knob.

For measurement work, choose sine: it concentrates all its energy at one frequency, so when something rattles, hums, or resonates in response, you know precisely which frequency provoked it. The harmonic-rich shapes are for listening experiments and sound design — a square wave through a small speaker is a quick way to hear what a speaker's high end is doing.

Young human hearing nominally spans 20 Hz to 20 kHz — about ten octaves, coincidentally close to a piano's range. The bottom end is felt as much as heard; the top end is where age quietly negotiates. Presbycusis, the standard age-related roll-off of the highest frequencies, takes most ears from a ~20 kHz ceiling in the teens down to 15-17 kHz by middle age, while the speech band between roughly 300 Hz and 3 kHz stays intact. Sweep upward slowly and you'll find your own cliff, give or take the honesty of your speakers.

Physics draws the top boundary firmly. Digital audio at the standard 44,100 Hz sample rate can represent frequencies only up to half that — 22,050 Hz — which is Nyquist's theorem wearing its most practical hat. That's why this generator's dial ends at 22,000 Hz: beyond it, the mathematics itself stops being representable, and the "ultrasonic" tracks sold on wellness storefronts are either inaudible or, on closer inspection, not actually ultrasonic at all.

At the low end, speakers are usually the limit rather than ears. Laptop speakers roll off steeply below about 150 Hz; phone speakers barely reach 400 Hz honestly. A 40 Hz tone through desktop monitors is a deep, physical hum; the same tone through a phone is a faint tapping that mostly isn't there. If a low tone vanishes on your hardware, suspect the drivers before your cochlea — headphones tell the truth down to 20 Hz more often than any speaker can.

A sweep slides the tone from one frequency to another over a duration you set. Linear sweeps advance the same number of hertz per second; logarithmic sweeps spend the same time on every octave. For ears and for trouble-hunting, logarithmic is the default that matters — 20 Hz to 40 Hz is as wide a musical interval as 10 kHz to 20 kHz, and a log sweep treats them as equals instead of sprinting through the entire low end in the first half-second.

The technique is old and reliable: run a slow log sweep upward and listen for anything that answers. Rattles step forward — a window latch, a drawer pull, a picture frame — each one buzzing at the particular frequency that matches its mechanical resonance. Room modes reveal themselves as swells and hollows in the sweep's loudness, the standing waves that make one bass note boom in the back of a room while its neighbor vanishes. Speaker flaws announce themselves as buzzes, dropouts, or the tweeter going suddenly silent while the sweep continues.

Basic room acoustics is checkable with a tape measure and this dial. Sound travels about 343 meters per second in room-temperature air, so a room dimension of L meters has its strongest axial standing wave at 343 ÷ (2L) Hz — a 3-meter wall-to-wall span produces a mode near 57 Hz. Sweep slowly through the 50-70 Hz region, find the note that booms, and you've located your room's geometry in the frequency domain. Bass traps and furniture placement are then engineering rather than folklore.

Play 200 Hz in one ear and 204 Hz in the other through headphones and most listeners perceive a slow pulsation at 4 Hz — a binaural beat, the auditory system's response to two slightly mistuned streams. The dual-tone mode exists for exactly this experiment, and it's a genuinely interesting piece of perceptual science you can run on yourself with a slider.

The honest footnote: binaural beats have been studied for decades as a route to relaxation, focus, and sleep assistance, and the controlled results are mixed to modest — effects where they appear tend to be small and inconsistent across people. What's solid is the phenomenon itself; what isn't solid is the catalog of specific frequencies marketed as brain-state switches. Enjoy the pulsation, treat the mood claims as folklore with a lab coat on, and the dial remains fun either way.

Musicians use the same physics through the air instead of headphones: two tones sounding together in one room produce a physical beat at the difference frequency, which is how brass sections and string sections tune in unison — you chase the wobble until it stops. Two oscillators, 440 and 443 Hz, in a room produce a wobble at 3 Hz you can count like a metronome. Tuning by beats is five centuries old and still the fastest way to hear what "in tune" means.

Thirty seconds of sweeping did the work of an hour of guessing. The 120 Hz finding is the classic North American hum pattern — anything with a small transformer vibrates at twice the mains frequency, so 120 Hz suspects are power bricks, dimmers, and chargers; in 50 Hz countries the same logic sends you hunting at 100 Hz. The steady-tone confirmation step is what separates a guess from a diagnosis.

The hearing line deserves a gentle framing. Noticing that 17.5 kHz is gone is trivia, not pathology — the speech and music you actually live in sits far lower, and gradual high-frequency roll-off is the standard human package deal. The sweep is worth running once every few years the way a ruler is worth owning: not medical equipment, just an honest measurement you can compare against later.

• Home-studio owners hunting room modes, rattles, and the monitor that flatters them — a 30-second sweep is the cheapest acoustic measurement ever made.
• Musicians and instrument techs tuning by beats, testing intonation, or generating reference pitches; for tempo rather than pitch, the Online Metronome is the companion tab.
• Guitarists checking where their amp starts to break up, and anyone verifying that a pickup or pedal passes the frequencies it claims to — string tuning itself belongs to the Online Guitar Tuner.
• Audio engineers burning in and matching speakers, or producing test signals for level calibration before a session — then leveling the results with the MP3 Volume Booster.
• Physics and music teachers demonstrating standing waves, beats, octaves, and Fourier's idea with a projector and one web page.
• Podcasters and home recorders checking their chain: this page confirms the speakers, and the Online Voice Recorder confirms the microphone.
• People masking tinnitus — broadband noise and gentle tones genuinely help many sufferers focus away from the ringing, an application with better evidence than most wellness uses of sound.
• Anyone with a hum, a rattle, or a mystery sound and a house to search room by room.

The honest gap is output calibration. A bench generator tells you it's delivering 500 millivolts peak-to-peak; this page tells you it's delivering 440 Hz and lets your ears negotiate the rest. For acoustic testing, psychoacoustics, education, and every hunt on this page, the gap never matters. The day you need volts, you need different equipment — and you'll know it.

The privacy paragraph on most tool pages is about files. This one has none to protect — there is no upload because there is no audio file until you render one, and there is no input worth privacy beyond your choice of frequency. The oscillator is computed on your machine, plays on your machine, and stops when the tab does. Nothing about your hearing test, your sweep, or your hum hunt is transmitted anywhere, because there was never anything to transmit.

Once the page has loaded it works with the network switched off, which — beyond the general principle — is the practical guarantee that your studio laptop can stay airplane-mode-clean during a session. Instruments that are pure local computation are the easiest tools on the internet to trust: the entire apparatus is mathematics running in front of you, at a volume you chose.

Sound work is a bench with several instruments on it. This one generates; the Online Metronome counts; the Online Guitar Tuner listens; the MP3 Volume Booster corrects levels on finished files; the Online Voice Recorder captures new ones. Open the right tab for the job at hand and close it without a trace — every tool on this bench runs entirely on your machine.