How to use it
- Turn your device volume down, then press Play.
- Pick a frequency with the slider (it is logarithmic, so each octave takes the same width), type it to a hundredth of a hertz, step by 1 Hz or a semitone, or tap a preset. The note name and how many cents it is from that note are shown under the number.
- Choose the wave shape and level. Sweep glides from one frequency to another over a set time; Different tone in each ear plays one frequency on the left and another on the right.
- Download WAV saves the current tone, sweep or pair as a 48 kHz, 16-bit WAV file.
What each wave shape sounds like
A sine wave is a single frequency and nothing else. Square, sawtooth and triangle waves add overtones at whole-number multiples of the frequency, which is why they sound brighter or buzzier at the same pitch. Browsers build these from a limited set of overtones that stops below the highest frequency the audio can carry, so a high square wave does not fold back into false, out-of-tune tones.
| Wave | Overtones (measured at 1 kHz, relative to the 1 kHz fundamental) | Theory |
|---|---|---|
| Square | 3 kHz -9.5 dB, 5 kHz -14.0 dB, even ones below -103 dB | odd harmonics at 1/n: −9.5, −14.0 dB |
| Sawtooth | 2 kHz -6.0, 3 kHz -9.5, 4 kHz -12.0, 5 kHz -14.0 dB | all harmonics at 1/n: −6.0, −9.5, −12.0, −14.0 dB |
| Triangle | 3 kHz -19.1 dB, 5 kHz -28.0 dB | odd harmonics at 1/n²: −19.1, −28.0 dB |
Sweeps and two-tone mode
A logarithmic sweep spends the same time on every octave, which is how hearing and loudspeaker tests are usually run; a linear sweep moves the same number of hertz each second and rushes through the low end. In our 10-second sweep from 20 Hz to 20 kHz, the logarithmic version was at 632.2 Hz halfway through (the geometric middle is 632.5 Hz) and the linear one at 10009.6 Hz.
Two-tone mode sends one frequency to the left channel and another to the right. With headphones, two close frequencies such as 200 and 210 Hz are heard as a slow 10-per-second pulsing called a binaural beat; through speakers the tones mix in the room and you hear an ordinary acoustic beat instead. Whether they do more than that is unsettled: a 2023 systematic review of 14 EEG studies found 5 consistent with the claim that the beat makes brain activity follow it, 8 contradicting it and 1 mixed, and a 2026 meta-analysis rated the evidence for pain relief from theta-range beats as low-certainty. Treat the mode as a listening experiment, not a treatment.
What we tested
On October 15, 2026, in Chromium 141.0.7390.37, we rendered tones with the page’s own code and measured the files:
| Check | Result |
|---|---|
| Frequency, 30 tones from 20 Hz to 21 kHz | largest error 0.0 Hz |
| Level of sine WAVs set to −12 dBFS | RMS -15.01 dBFS at every frequency (a sine’s RMS is 3.01 dB below its peak) |
| False tones (aliasing) | nothing above -98.1 dB between the overtones, including 7 kHz square and sawtooth waves |
| Start and end | 15 ms fade in and out: no sample-to-sample jump larger than in the steady tone, so no clicks |
| Sweeps | logarithmic and linear sweeps within 0.03% of the target frequency at the midpoint |
| Two tones | left 200.0 Hz, right 210.0 Hz |
| Note names | 206 frequencies, 0 differences from the formula (A4 = 440 Hz) |
One limit we found: the browser’s own oscillator, which plays the tone live, rolls off at the very top. At a 48 kHz output rate Chromium played 20 kHz -2.1 dB and 21 kHz -4.8 dB below the set level (19 kHz and below were exact). The downloaded sine WAV is computed directly instead, so its level is exact at every frequency; use it for hearing-limit or speaker tests at the top of the range.
Tips
- Hearing of high frequencies fades with age, and small speakers cannot reproduce deep bass; silence at either end of the range may be the speaker, your ears, or both.
- To find a rattle in a room or car, sweep slowly through 30 to 200 Hz and listen for the frequency where it buzzes.
- Use the note readout to tune by ear: a tone 10 cents off is close enough for most listeners not to notice.
- This is not a medical hearing test. If you notice changes in your hearing, see an audiologist.
Sources
Checked on .
- W3C: Web Audio API 1.1, OscillatorNode and PeriodicWave
- ISO 16:1975 Acoustics: Standard tuning frequency (A4 = 440 Hz)
- MDN Web Docs: OfflineAudioContext
- Ingendoh, Posny and Heine (2023), Binaural beats to entrain the brain? A systematic review, PLOS ONE 18(5): e0286023 (PubMed 37205669)
- Fatima et al. (2026), Efficacy of theta binaural beat therapy on pain, cognition and anxiety in adults: meta-analysis, Explore 22(5): 103471 (PubMed 42349368)
- NIDCD: Age-Related Hearing Loss (Presbycusis)
Frequently Asked Questions
Built by Derek Giordano · Part of Ultimate Design Tools