How to use the spectrum analyzer
- Press Use microphone to analyse live sound, or drop an audio file (MP3, WAV, M4A and others your browser can play).
- Watch the spectrum: frequency runs from 20 Hz on the left to 20 kHz on the right on a logarithmic scale, and height shows the level in decibels.
- Switch to Spectrogram to see frequencies over time as a scrolling colour map. Use Peak hold, Freeze and a larger FFT size for detail; hover to read any frequency and note.
What a spectrum analyzer shows
Any sound can be broken down into a mix of pure frequencies. The analyzer uses a Fast Fourier Transform (FFT) to do this many times per second. A larger FFT size gives finer frequency resolution (useful for low notes and hum) at the cost of slower response. The peak readout shows the loudest frequency, refined between FFT bins, and the nearest musical note, so you can identify the pitch of a hum, whistle or instrument.
Typical uses include finding the frequency of mains hum (50 or 60 Hz and its harmonics), checking feedback frequencies in a PA system, seeing which frequencies a voice or instrument produces, spotting a lack of bass or treble in a recording, learning about harmonics in a physics class, and identifying high-pitched whines from electronics. Your device's microphone shapes what it hears: phone microphones often roll off below 100 Hz and above 15 kHz. All processing happens locally with the Web Audio API.
Why does a single note show several peaks?
Real instruments produce harmonics at whole-number multiples of the fundamental frequency.
Can I analyse a video's audio?
Yes. Drop a video file; its soundtrack plays and is analysed.
What does the spectrogram colour mean?
Blue is quiet and red is loud, for each frequency over time.