Tone generator

How to use the tone generator

1. Type a frequency in the box, drag the slider, or nudge it with −10, −1, +1 and +10. The nearest note and how many cents off it you are show underneath.
2. Press Play. The volume starts at 10 %; raise it slowly. Change the frequency, wave or channel while it plays.
3. Tap + Add tone for up to four tones at once. Each tab keeps its own frequency, wave and channel, so you can play a chord, a beat between two close tones, or 440 Hz on the left against 660 Hz on the right.
4. For a sweep, set where it starts and ends, how long it takes and the scale, then press Play sweep. The frequency it has reached is shown as it goes.
5. For noise, pick white, pink or brown, set the sleep timer if you want it to fade out by itself, and press Play noise.

Frequencies and note names

The page names the nearest note of the equal-tempered scale, where each semitone is a factor of 2^1/12 (about 1.0595) and a cent is a hundredth of a semitone. With A4 = 440 Hz, middle C (C4) is 440 × 2^−9/12 = 261.63 Hz, and 450 Hz reads as A4 +39 cents. Change the A4 box (380 to 500 Hz) to tune to 442 Hz or 432 Hz and every name moves with it.

The slider is logarithmic because pitch is: each step of the slider multiplies the frequency by the same amount, so 20–200 Hz gets as much room as 2,000–20,000 Hz, and its middle is 141 Hz. Use the number box when you need an exact value, decimals included.

Sine, square, sawtooth and triangle

A sine is a single frequency and nothing else. The others add harmonics, whole-number multiples of the frequency: a square wave has the odd ones (3×, 5×, 7×) at 1/3, 1/5, 1/7 of the strength, a sawtooth has all of them at 1/n, and a triangle has the odd ones falling much faster, at 1/n², so it sounds close to a sine. A 1,000 Hz square therefore also sends 3, 5 and 7 kHz to your speakers. The browser builds these waves without the harmonics above half the sample rate, so high square waves do not alias into stray tones. Square and sawtooth are turned down a little so that switching waves does not jump in loudness.

Linear and logarithmic sweeps, worked out

A logarithmic sweep spends the same time on every octave. From 100 to 1,000 Hz over 10 seconds, it is at 100 × 10^t/10 Hz: 200 Hz after 3.0 s, 400 Hz after 6.0 s, and at the half-way time, 5 s, at √(100 × 1,000) = 316 Hz. A linear sweep adds the same number of hertz every second, so it is at 550 Hz half-way and races through the low octaves. Log sounds even to the ear and is the usual choice for finding a rattle or a room resonance; linear is handy for scanning a narrow band, such as 50 to 120 Hz for a subwoofer.

White, pink and brown noise

White noise has equal power in every hertz. Because each octave up has twice as many hertz, it sounds bright and hissy. Pink noise falls 3 dB per octave, which gives every octave the same power; it sounds like steady rain and is used to check speakers by ear. Here it comes from white noise through Paul Kellet's filter, which stays within a small fraction of a dB of the 3 dB slope across the audible range. Brown noise (after Robert Brown and Brownian motion, not the colour) is white noise added up over time, which falls 6 dB per octave; it is a low rumble, like surf or a waterfall. All three are made fresh in your browser as a 10-second loop with its ends blended, and set to the same RMS level so switching does not jump in loudness.

The sleep timer counts on the audio clock and fades the noise over its last minute. Many people find a steady sound helps them fall asleep or blocks out an office; it is a comfort, not a treatment, and it is best kept quiet.

What it cannot do

• It plays what you set, but your speakers or headphones decide what you hear. Many cannot play below about 50 Hz or above about 16 kHz; phone and laptop speakers often give little below 100–200 Hz. A 1 Hz or 5 Hz tone is real, but no ordinary speaker makes it audible.
• Phones may stop the sound when the screen locks or the browser goes to the background, and an iPhone with its silent switch on may play nothing. Keep the page open on screen for a sleep timer.
• It does not measure anything. It cannot tell whether a speaker, your room or your ears are the reason a tone sounds quiet, and it is not a medical device.
• Frequencies are exact in the signal, but sound cards run at 44.1 or 48 kHz, so tones close to 20 kHz are made from only 2–3 samples per cycle and some cheap outputs distort them.
• The left/right buttons send sound to one channel. If your device is set to mono audio, or one Bluetooth earbud is playing both, you will hear it in both ears anyway.

Privacy

Everything is made in this page with Web Audio; no sound files are downloaded and nothing you set is sent anywhere. The page counts an anonymous page view and, the first time you play a tone or noise, the fixed words tone-play or noise-play, never the frequency or settings.

Questions

How do I test my left and right speakers?

Pick a tone such as 440 Hz, tap Left and press Play: only the left speaker or earbud should sound. Tap Right and it moves across. If both sides play or they are swapped, check the cable, the balance setting of your computer or phone, and whether mono audio is on in its accessibility settings.

What is the difference between white, pink and brown noise?

White noise has the same power in every hertz, so it sounds hissy. Pink noise has the same power in every octave (3 dB less per octave up), which sounds more even, like steady rain. Brown noise falls 6 dB per octave and sounds deep, like a waterfall or a distant roar.

What frequency is A4?

A4, the A above middle C, is 440 Hz in standard concert pitch (ISO 16). Some orchestras tune to 442 or 443 Hz and some musicians prefer 432 Hz; set the A4 box and the note names follow.

Why can I not hear a 20 Hz or 18,000 Hz tone?

Usually because the speaker cannot play it: phone and laptop speakers often give little or nothing below 100–200 Hz, and many headphones roll off above 16 kHz. Most adults also hear less of the highest frequencies as they get older. The page plays the tone either way; it cannot tell which one is the limit.