What this online spectrum analyzer can do
Most free spectrum analyzers give you a bouncing graph and leave it there. This one is built to give you numbers you can trust. It runs a full FFT analysis inside your browser, so there is nothing to install and nothing gets uploaded.
Feed it a microphone, an audio file or a built-in test signal, and you can read the frequency in Hz and the level in dB straight off the graph.
Three ways to bring audio in
Tap Microphone and the browser asks for permission right away, so there is no extra Play press. If your computer has more than one input, a device picker lets you choose between a laptop mic, a USB interface or a headset.
Prefer a recording? Drop an audio file onto the upload area, or start with a built-in sample such as a clean 1 kHz sine, which is handy for checking that the readings behave.
Nine views, one signal
The tabs above the graph switch the display instantly, even while audio is playing. Bars, Line, Filled, Dots, Gradient and Mirror all show the live spectrum, just drawn differently. Octave bands group the energy the way your ears and EQs do.
Waterfall and Spectrogram add time, so you can watch a note decay or catch a hum that comes and goes. The spectrogram can be saved as an image, and four colour maps are included: Spectrum, Viridis, Magma and Grayscale.
Axes you can actually read
The graph is labelled in Hz and dB from the start, not left as a plain black box. Zoom and pan to inspect a narrow band, then switch on cursors A and B to measure the gap between two peaks in hertz and decibels. With Cursors on, they land on the two strongest peaks by themselves.
Settings for people who care about accuracy
Choose an FFT size from 2048 to 32768 points. Larger sizes separate close frequencies better but react more slowly. Pick a window (Hann, Hamming, Blackman, Blackman-Harris or Flat-top), an averaging mode (off, exponential, linear, RMS or max hold), 50, 75 or 90 percent overlap, and A, C or no weighting.
Levels can be shown in dBFS or dB SPL, and you set the dB floor and ceiling yourself.
Measuring the level of a single tone? Try the Flat-top window. Trying to separate two close frequencies? Hann or Blackman with a large FFT works better.
Freeze, Peak Hold and a table that keeps score
Freeze stops the picture so you can study it. Peak Hold draws the highest level reached at each frequency in a different colour from the live wave, and it works even when playback is paused. Reset peaks wipes the trace.
Each time you freeze or switch Peak Hold on, the Strongest spectral peaks table records that moment with frequency, level, nearest note and cents. You can compare several snapshots, then clear the table whenever you want a fresh start.
Harmonics, distortion and noise
Under the graph, the harmonic analysis lists the fundamental and harmonics H2 to H10 with their level relative to the fundamental, plus THD, THD+N and SNR. It is useful for checking an amplifier, a synth patch or a whole recording chain.
Export what you measure
The Report menu saves the graph as a PNG image, or the data as JSON, CSV, XML or plain text. The full-spectrum CSV and JSON include every FFT bin. Each report stores the sample rate, FFT size, window and other settings, so someone else can reproduce your measurement. The Share button creates a link and QR code for your current settings.
Who uses it, and for what
- Mixing and mastering: find boxy low-mids, a harsh 3 kHz or a stray resonance before it reaches the master.
- Room and speaker tuning: play a sweep from our Sweep Generator and see where the room adds or cancels bass.
- Hum and noise hunting: 50 or 60 Hz and its harmonics stand out immediately.
- Researchers and students: export clean data with the settings attached.
- Checking MP3 files: a sharp cliff near 16 kHz usually points to a low-bitrate encode.
Everything runs locally in your browser, so your microphone input and audio files are never sent anywhere. The layout is touch friendly as well, which means the same tools work on a phone or tablet.