Frequency detector — free hertz meter for sound

What is a frequency detector?

A frequency detector, also called a hertz meter or frequency meter, listens to a sound and reports how many cycles that tone completes each second. This one uses your microphone and an autocorrelation pitch detector to estimate the fundamental frequency, then shows it in hertz (Hz). A reading of 440 Hz means the tone repeats 440 times per second, which is the concert pitch A4. It is a sound frequency meter for one steady tone, from about 50 Hz to 2000 Hz. It is not an electrical multimeter, a radio tuner, or a spectrum analyzer that graphs every frequency in a mix.

What the hertz meter shows

A browser frequency reader for a single acoustic tone: hertz first, with the nearest musical note and cents beside it.

1. Hertz as the main readout: The large number is the measured frequency in Hz, updated while the tone holds. Use it when you care about the rate of the sound, not only its note name.
2. Nearest note and cents: Under the hertz value, the meter names the closest equal-tempered pitch (A4 = 440 Hz) and the offset in cents. That tells you whether a tuning fork, hum, or instrument is sitting on the reference or a little sharp or flat.
3. Fundamental frequency, about 50–2000 Hz: The algorithm looks for the repeating period of one tone. A 1 kHz test tone, middle C at 261.6 Hz, and a low guitar E at 82.4 Hz are inside that span. Energy above 2000 Hz, and sounds with no clear pitch, will not produce a stable reading.
4. Reference tones on the page: Concert A (440 Hz), middle C (261.6 Hz), A3 (220 Hz), guitar low E (82.4 Hz), and a 1 kHz tone are listed so you can compare what you hear with a known frequency.
5. Microphone audio stays on the device: The frequency measurement runs in the browser with the Web Audio API. The microphone stream is not recorded or uploaded.

How to measure the frequency of a sound

Use the frequency meter on one sustained tone. A noisy room or several notes at once will not settle on a single hertz value.

1. 1. Start the frequency meter and allow the microphone: Click Start Frequency Meter and accept the browser prompt. No audio is stored. If the mic is muted or in use by another app, the meter stays on "Listening."
2. 2. Hold one steady tone near the microphone: Hum, whistle, strike a tuning fork, or play a single string or key. Keep the pitch still for about a second. Vibrato, speech, and chords make the hertz value jump because the fundamental is changing or is not unique.
3. 3. Read Hz, then the note: The large figure is the frequency measurement in hertz. The smaller line is the nearest note and how many cents you are from it. Green cents (5 or fewer) means you are very close to the standard frequency of that note.

Get a stable hertz reading

The meter follows the strongest repeating period in the microphone signal.

1. Measure one source at a time: A frequency reader needs a single periodic tone. Turn off fans if you can, and do not talk over the tone you are measuring.
2. Put the mic close to a quiet source: A tuning fork or acoustic instrument works at roughly 15–30 cm. A loud amplifier can overload the microphone and smear the period estimate.
3. Use a known tone to check the meter: Play 440 Hz from the Tone Generator in another tab, or use a tuning fork, and confirm the readout lands near 440.0 Hz. Small deviations of a few hertz are normal with a laptop microphone.
4. Do not use it for mains voltage or radio: This tool measures airborne sound. It does not probe a wall outlet, a circuit, a Wi-Fi channel, or a CPU clock. A loud 50 Hz or 60 Hz hum can show up only if the microphone actually hears that hum.

Sources & References

References for the hertz unit and the browser audio analysis this frequency meter uses.

• Hertz — the SI unit of frequency

  “The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second.”

  The large readout is that unit: cycles of the detected tone per second. Wikipedia also notes that people hear the frequency of a sound as pitch, and that each musical note corresponds to a particular frequency. en.wikipedia.org/wiki/Hertz

• AnalyserNode — time-domain audio data

  “The AnalyserNode interface represents a node able to provide real-time frequency and time-domain analysis information. It is an AudioNode that passes the audio stream unchanged from the input to the output, but allows you to take the generated data, process it, and create audio visualizations.”

  Microphone samples are read from an AnalyserNode in the time domain. The meter then estimates the period of that waveform and converts the period to hertz. developer.mozilla.org/en-US/docs/Web/API/AnalyserNode

Frequently Asked Questions

Have questions? We have answers.

Related tools

Explore other diagnostic tools that pair well with this page.

• Tone Generator→Tone generator online—play pure sine, square, triangle, or sawtooth tones from 20 Hz to 20 kHz for speaker and audio testing.
• Pitch Detector→Pitch detector online—detect the pitch of any sound with your microphone. See note, frequency, and tuning accuracy.
• Note Finder→Note finder online—identify the music note you sing or play. See the note name, octave, and frequency.
• Voice Pitch Analyzer→Pitch analyzer online—find the note you are singing and see the octave and cents.
• Sound Test→Sound test online—check your speakers, test left/right channels, and verify stereo balance.
• Mic Test→Mic test online—check your microphone with live waveform and volume level.