What frequency is middle C?

Middle C is C4 at 261.63 Hz in equal temperament with A4 = 440 Hz. The C4 preset plays it, and the note readout shows C4 at +0 cents.

A4, often called concert A, the A above middle C. Doubling a frequency gives the same note one octave up, so the A5 preset at 880 Hz reads A5 and 220 Hz reads A3, both at +0 cents. 442 Hz reads A4 at +8 cents.

How do I test speakers or headphones with a tone?

Start at a low volume and play the 1 kHz preset, then raise the volume slowly. To look for the ends of your range, play a sweep from 20 Hz to 20,000 Hz and note where you stop hearing it. Small speakers and earbuds may not reproduce the lowest frequencies, and what you hear at the top of the range depends on the listener.

What does the sweep do?

It glides from the start frequency to the end frequency in a straight line in hertz, over 1 to 10 seconds. The defaults are 200 Hz to 2,000 Hz over 5 seconds. Each end is limited to 20 to 20,000 Hz.

Can I download the tone as a WAV file?

Yes. Save as WAV renders the current settings, sweep and fades included, to a mono 16-bit file at 44.1 kHz without playing them. It lasts the chosen duration plus the release, or 10 seconds plus the release when the length is continuous: the default 10.1 seconds is 890,864 bytes, about 0.85 MB.

How accurate is the note readout?

It is arithmetic: 12 × log₂(frequency ÷ 440) semitones from A4, rounded to the nearest note, with the remainder in cents. 432 Hz reads A4 at -32 cents. It describes the tone this page plays, not what your speakers produce.

Audio Tone Generator

Play a sine, square, sawtooth, triangle or noise tone from 20 Hz to 20,000 Hz, sweep it, read the nearest note and save it as a WAV file. How it works

Frequency

440 Hz

A4 (+0¢)

20 Hz20 kHz

Waveform

Envelope

Attack0.01s

Release0.10s

Frequency Sweep

DurationContinuous

Volume50%

Continuous saves 10 s plus the release, mono, 44.1 kHz, about 0.85 MB. Rendered in this browser.

Space Play/Stop · ↑↓ ±1 Hz · Shift+↑↓ ±100 Hz

About the Audio Tone Generator

440 Hz is the note A4, the usual tuning pitch. This tone generator plays any frequency from 20 Hz to 20,000 Hz as a sine, square, sawtooth or triangle wave, or as white noise, names the nearest equal-tempered note and saves the tone as a WAV file: 261.63 Hz reads C4 and 1,000 Hz reads B5, 21 cents sharp.

Frequency to nearest note

Frequency	Nearest note	Cents
55 Hz	A1	+0
110 Hz	A2	+0
220 Hz	A3	+0
261.63 Hz	C4	+0
329.63 Hz	E4	+0
392 Hz	G4	+0
440 Hz	A4	+0
523.25 Hz	C5	+0
880 Hz	A5	+0
1,000 Hz	B5	+21
1,760 Hz	A6	+0

As the tone generator's note readout shows them, with A4 = 440 Hz and equal temperament. Cents are rounded; 100 cents is one semitone.

How to use this tool

Type a frequency from 20 to 20,000 Hz, drag the slider, or press a preset such as A4 or 1 kHz.
Choose a waveform and keep the volume low to start.
Press Play, or the space bar. Set a length of 5, 10, 30 or 60 seconds, or leave it continuous.
For a sweep, switch Sweep on and set the start and end frequencies and the time, from 1 to 10 seconds.
To keep the tone, press Save as WAV. The file has the chosen length plus the release, or 10 seconds when the length is continuous.

Frequently asked questions

What frequency is middle C?: Middle C is C4 at 261.63 Hz in equal temperament with A4 = 440 Hz. The C4 preset plays it, and the note readout shows C4 at +0 cents.
What note is 440 Hz?: A4, often called concert A, the A above middle C. Doubling a frequency gives the same note one octave up, so the A5 preset at 880 Hz reads A5 and 220 Hz reads A3, both at +0 cents. 442 Hz reads A4 at +8 cents.
How do I test speakers or headphones with a tone?: Start at a low volume and play the 1 kHz preset, then raise the volume slowly. To look for the ends of your range, play a sweep from 20 Hz to 20,000 Hz and note where you stop hearing it. Small speakers and earbuds may not reproduce the lowest frequencies, and what you hear at the top of the range depends on the listener.
What does the sweep do?: It glides from the start frequency to the end frequency in a straight line in hertz, over 1 to 10 seconds. The defaults are 200 Hz to 2,000 Hz over 5 seconds. Each end is limited to 20 to 20,000 Hz.
Can I download the tone as a WAV file?: Yes. Save as WAV renders the current settings, sweep and fades included, to a mono 16-bit file at 44.1 kHz without playing them. It lasts the chosen duration plus the release, or 10 seconds plus the release when the length is continuous: the default 10.1 seconds is 890,864 bytes, about 0.85 MB.
How accurate is the note readout?: It is arithmetic: 12 × log₂(frequency ÷ 440) semitones from A4, rounded to the nearest note, with the remainder in cents. 432 Hz reads A4 at -32 cents. It describes the tone this page plays, not what your speakers produce.

Speaker checks, hearing range and tuning

The tone generator plays a steady tone from 20 Hz to 20,000 Hz. Use it to check speakers or headphones, find the highest pitch you can still hear, tune an instrument against a reference note, or run a frequency sweep. Pick a sine, square, sawtooth or triangle wave, or white noise, then set the volume, a fade in and out, and a length of 5, 10, 30 or 60 seconds or continuous. Presets give middle C, E4, G4, A4, A5 and 1 kHz. Save as WAV writes the same settings to a file, for a video editor or another device. Start quiet, especially with headphones.

How the tone and the note are worked out

The sound comes from a Web Audio oscillator, not a recording. A sine wave is one frequency; square, sawtooth and triangle waves sound different at the same pitch, and white noise has no single pitch.

The note readout uses A4 = 440 Hz and equal temperament:

semitones from A4 = 12 × log₂(frequency ÷ 440)

The page shows the nearest note and the gap in cents (100 cents = one semitone). 261.63 Hz is 9 semitones below A4: C4, middle C, at +0 cents. 1,000 Hz reads B5 at +21 cents, and 432 Hz reads A4 at -32 cents.

Attack and release set how long the volume takes to rise and fall; 0 still ramps over 5 ms, so the tone does not click. A sweep moves in a straight line in hertz from the start to the end frequency, over 1 to 10 seconds.

Save as WAV renders the settings offline, mono, 16-bit, at 44,100 samples a second: bytes = 44 + seconds × 44,100 × 2. The length is the chosen duration plus the release, or 10 seconds plus the release when it is continuous, so the default 10.1 seconds is 890,864 bytes (about 0.85 MB).

Fun Fact: A London conference in May 1939 recommended A = 440 Hz as standard pitch; ISO 16 formalised it in 1975.