How to use it
- Press Start analyzer and allow the microphone.
- Make a sound: whistle, hum or play a tone from another device. A pure tone shows as one narrow peak.
- Use Freeze to hold the graph and read the loudest frequency; Resume continues.
- Press Stop to turn the microphone off.
What you see
Each column is the loudest FFT bin inside that slice of the log axis, smoothed over time by the browser (smoothing constant 0.7). Bar height maps −100 dB to −10 dB (relative to digital full scale) onto the height of the graph. The “loudest frequency” is the highest bin from 20 Hz upward, shown only above −80 dB so background noise does not produce a random number.
Worked example
A tone of 1 000 Hz at a 48 kHz sample rate falls in bin 1000 × 8192 / 48000 ≈ 170.7, so the peak shows about 1 000 Hz (to within one bin, 5.9 Hz). On the log axis it sits at log(1000 / 20) / log(20000 / 20) = 56.6 % of the width.
Tips
- Mains hum appears as peaks at 50 or 60 Hz and their multiples.
- Hold a phone with a tone close to the microphone to check the graph against a known frequency.
- This is a visual aid, not a calibrated measuring instrument.