Test Tones
Play a clean 1 kHz or 50 Hz sine and the same tone with added harmonics, then try a blind check of which copy is distorted. Also play an equal-loudness sweep from 20 Hz to 20 kHz, plus pink, white and brown noise, reference tones and a 19 + 20 kHz pair. Download any of them as WAV. This does not measure THD.
Start quiet and raise the volume slowly. Pure tones and high frequencies are tiring and can damage hearing and tweeters. Headphones give the most reliable results.
1. Clean sine and added harmonics
The clean button loops a 1 kHz sine with no added harmonics. Each percent button loops that same sine plus harmonics at 3 kHz. The percent is √(H2² + H3² + …) / H1 for those harmonics in the generated tone. The decibel line is that ratio, not the volume. This is not a THD measured from a recording, and the microphone is not used. Start at 5% and compare it with the clean sine.
The bars are rough published ranges, not a reading from this page. Many amplifier spec sheets quote under 0.1%, and some quote under 0.01%. A sheet that boasts 0.0005% instead of 0.005% is selling a gap you are very unlikely to hear. The 0.001% and 0.01% buttons are for comparing with the clean sine. If they sound different, suspect expectation, then use the blind check.
Blind listening check
Press Start, then play Sample A and Sample B yourself. On the 1 kHz sine, with the harmonic mix above, one sample is clean and one has 1% added harmonics, picked at random. Say which is distorted. Changing the tone or the mix during a trial stops the sound and cancels that trial.
2. Equal-loudness sweep
Your ears are not flat. Fletcher and Munson showed in 1933 that low bass and the top octave need far more sound pressure to seem as loud as the midrange, and that the effect grows at low volume. ISO 226 is the modern version of their curves. With compensation on, the sweep boosts the extremes (up to +24 dB relative to 1 kHz) so a flat system sounds about even; a range that drops away or jumps out is your gear or your hearing. With it off, the sweep is flat in level and the bass and top end will seem to fade. The chart matches the checkbox. Changing the length or the checkbox stops a sweep that is already playing.
3. Test signal library
Downloads are 48 kHz, 24-bit mono WAV.
Equal energy per octave. The standard for setting speaker levels and judging tonal balance.
Equal energy per hertz, so it sounds bright and hissy. Good for spotting rattles and treble problems.
Falls 6 dB per octave. A low rumble that works the woofer and exposes buzzing in the bass.
The classic calibration tone. Set an SPL meter or recorder level against a known digital level.
Concert pitch A for tuning instruments, and a quick check that playback runs at the right speed.
Mains hum with its 120 and 180 Hz harmonics, as ground loops produce. Learn what to listen for.
Equal time per octave, the length of the chosen duration. Listen for buzzes, rattles and dropouts.
Bass, mid and treble at once. All three should be clearly audible and steady.
Most adults hear near silence. The file has no 1 kHz tone. A whine means something after the file added a difference tone. This page does not measure it.
Distortion, test signals and what they reveal
What THD and IMD are
Total harmonic distortion is the energy at whole multiples of a pure tone, divided by the tone itself. On this page, 1% means the combined added harmonics are 40 dB below the sine, and 0.01% means 80 dB below. Those percents are generated in the tone. They are not measured from a recording. Intermodulation distortion (IMD) happens when two tones mix inside a nonlinear device and create new tones at their sum and difference frequencies, which are not musically related to either tone and so are easier to notice.
How much distortion you can hear
On a lone sine, careful listeners often notice low-order harmonics somewhere around 0.1% to 1%, with the 3rd harmonic easier to spot than the 2nd. These are rough figures from listening studies, not a result this page calculates. Music hides distortion, because other sounds already fill the frequencies where the harmonics land. Speakers commonly produce plenty of bass distortion, which is why another zero on an amplifier spec sheet buys nothing you can hear here.
The 19 + 20 kHz IMD check
Most adults cannot hear 19 or 20 kHz, so a clean system plays this signal as near silence. The page plays only those two tones, each at -12 dBFS. It does not add a 1 kHz tone and it does not measure one. If an amplifier or tweeter is nonlinear, the two tones can mix and produce a 1 kHz difference that you may hear as a whine. That is your ear, not a distortion reading. Feeding ultrasonic content to drivers that distort on it can make playback worse, not better. The audio blind test covers whether you can hear hi-res at all.
Using the noise signals
Pink noise is the one for level matching: play it through each speaker in turn and set them equal on an SPL meter. White noise shows treble balance and hiss, and brown noise works the woofer to find rattles. The 1 kHz tone at -20 dBFS is a fixed reference for setting levels. For another listening sweep, try the frequency response test.
Safety
Keep the volume low. Steady tones are more fatiguing than music, and high-frequency and sweep signals can overheat tweeters at high power. The compensated sweep and the 19 + 20 kHz pair contain loud energy you may barely hear, so never turn up until you hear them.
Related tools
Compare files blind in the audio blind test, play any frequency with the tone generator, check how quiet your chain goes with the dynamic range test, and listen for where a tone fades with the frequency response test.
Frequently asked questions
What do the tone buttons play?
The clean button loops a 1 kHz (1000 Hz) or 50 Hz sine with no added harmonics. Each percent button loops that same sine plus harmonics. 2nd harmonic adds only twice the frequency (2 kHz or 100 Hz). 3rd harmonic adds only three times the frequency (3 kHz or 150 Hz). Mix adds the 2nd, 3rd, 4th and 5th. The percent is the combined level of those harmonics divided by the sine. The decibel figure under it is that same ratio, not the volume. The line under the buttons lists the harmonic frequencies for the mix you selected.
Is the percent a measured THD?
No. The page does not open the microphone and does not analyze a recording. It does not measure your amplifier, DAC, speakers or headphones. The percent is written into the generated tone. Your gear can add more distortion on the way out, and this page cannot hear that.
How do I stop the sound, and is 0% volume silent?
Press Stop, or press the button that is already playing. Leaving the page sets the gain to zero, stops the tone and closes the audio. Nothing plays until you press a play button. A download does not start playback. The volume slider starts at 20% unless a saved value is stored in this browser. At 0% the gain is exactly zero, so the tone is silent. The slider does not change system volume.
What does the blind check do?
It does not measure THD. You pick an added-harmonic amount, then press Start for 6 trials. Start does not play audio. You press Sample A and Sample B yourself. Each sample loops until you press it again, press the other sample, or press Stop. One is the clean sine and one has that added amount, in random order, using the frequency and harmonic mix on screen. You say which one is distorted. Choosing A or B, Cancel, or Change level also stops the sound. The score is how many you identified. Changing the test tone or the harmonic mix during a trial stops the sound and cancels that trial.
What does the equal-loudness sweep play?
A sine glide from 20 Hz to 20 kHz over 10, 20 or 30 seconds. It does not loop. With equal-loudness compensation on, bass and high frequencies are boosted relative to 1 kHz using a 60-phon approximation, and that boost is capped at 24 dB. The chart is that boost. With it off, the level stays flat and the chart is a flat line. The frequency shown while it plays is the glide position. Changing the length or the compensation box stops a sweep that is already playing. The WAV button saves that same sweep as 48 kHz, 24-bit mono and does not play it.
What do the library buttons and WAV downloads play?
Each library button plays the named signal for the duration on screen: pink, white or brown noise, a 1 kHz sine at -20 dBFS, 440 Hz at -12 dBFS, 60 Hz with quieter 120 Hz and 180 Hz harmonics, a flat 20 Hz to 20 kHz sweep at -12 dBFS, 100 Hz plus 1 kHz plus 10 kHz, or 19 kHz plus 20 kHz. Loop repeats a library signal until you stop it. Turning Loop off while one is playing lets that copy finish, then stop. Changing the duration stops a library signal that is already playing. The ladder always loops a 2 second tone until you stop it, and it ignores that Loop box. Ladder downloads are that 2 second tone as 48 kHz, 24-bit mono WAV, at the frequency, mix and percent on screen. Library downloads use the duration on screen, also 48 kHz, 24-bit mono. A download does not start playback. If the output sample rate cannot carry the highest frequency, playback stops and an error is shown instead of a tone with those partials removed.