Why autocorrelation instead of a transform peak?

Because autocorrelation finds the repeating period of the waveform, which is what the fundamental is. A transform peak simply reports the loudest frequency component, which in a harmonic-rich sound may well be the second or third harmonic rather than the fundamental itself.

What does the confidence figure mean?

It expresses how clearly one delay stood out from the alternatives in the autocorrelation. A high confidence means a single period was strongly indicated; a low one means the signal was noisy, polyphonic, or too short for a stable estimate, and the frequency should then be treated as a guess.

Why does it report nothing for some files?

The search range is bounded between fifty hertz and five kilohertz. Content outside that band produces no estimate, as does genuinely unpitched material such as noise or a drum loop, where no repeating period exists to find.

How accurate is the answer?

On a clearly pitched, sustained sound it is typically accurate to well within a hertz and is often more precise than reading a transform bin. On polyphonic or heavily processed material the confidence figure is the honest guide to how much to trust it.

Can it tell me the nearest note?

No, it reports a frequency only, so the conversion to a note is a separate step. That is deliberate: the frequency is the measurement, and mapping it onto a tuning system depends on which reference pitch you are working to.

Frequency Counter

You Might Also Need

Frequency Analyzer

Detailed frequency analysis

Spectrum Analyzer

Analyze frequency spectrum

Spectrogram Viewer

View time-frequency spectrograms

Waveform Visualizer

Visualize audio waveforms in real-time

Frequency Counter reports the fundamental frequency of a recording as a single number with a confidence percentage. It is the tool for a quick tuning check rather than for following a melody.

What is Frequency Counter?

The dominant readout gives the detected fundamental in hertz, with a confidence bar beneath it and a note of how many windows contributed to the result.

What the panel reports:

The fundamental frequency for the first channel, or a dash when nothing periodic is found.
A confidence between zero and one, displayed as a percentage and as a filled bar, so a weak estimate can be recognised rather than trusted blindly.
The number of analysis windows that contributed, or a note that no periodic signal was found in the search range of fifty hertz to five kilohertz.
A caption recording the file name, the sample rate, the channel count and the method used.

The estimate comes from normalised autocorrelation rather than from a transform peak. Autocorrelation compares the signal with a delayed copy of itself across a range of delays, and the delay that produces the strongest agreement corresponds to one period of the waveform. That matters because a frequency-domain peak can land on any harmonic, whereas the autocorrelation peak naturally aligns with the repeating period of the whole waveform, which is what the fundamental actually is. Detection is octave-safe, meaning the peak selection avoids the classic failure where a strong second harmonic is mistaken for the fundamental and the answer is reported an octave too high. The search range is bounded between fifty hertz and five kilohertz, which covers voice and most instruments while excluding the very low rumble and the very high partials that would confuse a period estimate, and the confidence figure reflects how distinct the winning delay was from the alternatives. Avoiding the octave error is the specific reason the period method is used here, because mistaking a strong second harmonic for the fundamental is the classic failure of naive detection and it produces an answer exactly double the truth. Nothing in the display asks you to trust the number without support, so the confidence bar and the window count are both shown and the search range is stated rather than left implicit. A frequency reported at low confidence is best treated as a hint to check by other means, while on a steady tone the estimate is normally the most precise figure available for the file.

Where the method has limits:

Only the first channel of a stereo file is analysed.
The result is a single figure for the whole file, so a changing pitch is averaged rather than tracked.
Content outside the fifty hertz to five kilohertz search range is reported as nothing found.
Polyphonic material can produce a confident but meaningless answer, since several fundamentals compete.
Percussive or noisy recordings typically produce low confidence rather than a useful number.
Nothing is exported, and no note name is given alongside the frequency.

Use it to check a tuning reference, confirm the pitch of a sustained note, or find out what a hum is actually sitting on. When the pitch changes through the material and the movement itself is the point, the frequency analyzer follows it segment by segment, and the spectrum view shows which harmonics are contributing to the sound.

How to use Frequency Counter

Drop an audio file onto the panel; the estimate is computed without any settings.
Read the frequency as the detected fundamental for the first channel of the file.
Check the confidence bar before relying on the value, especially for noisy or polyphonic material.
Confirm the result against the note you expected, or use it to identify an unexplained tone such as a hum.

When to use Frequency Counter vs related tools

Frequency Counter suits a quick, single-number tuning or identification check on material with a clear pitch. Frequency Analyzer follows the dominant pitch over time and lists it as measurable segments, and Spectrum Analyzer shows the harmonic content behind the fundamental. For a tone that needs to be examined as a time-frequency pattern, Spectrogram Viewer shows exactly where it sits.

Privacy & Security

This tool runs entirely in your browser — no data ever leaves your device. There is no server round-trip, no upload, no logging, and no account required. Your input is processed locally using client-side JavaScript and is never stored, transmitted, or accessible to anyone else. When you close the tab, everything disappears.