Real-Time Spectrum Analyser
Live FFT spectrum from your microphone, for identifying hum, resonance and room modes. Audio is analysed in the page and never recorded.
Click "Start Mic" to begin analysis
What the display is showing
The analyser applies a Fast Fourier Transform to short overlapping windows of incoming audio, decomposing each into its constituent frequencies. The horizontal axis is frequency, the vertical is magnitude in decibels.
There is an unavoidable trade-off built into this. A longer analysis window gives finer frequency resolution but poorer time resolution — you can know precisely what frequencies are present or precisely when they occurred, not both. This is the time–frequency uncertainty principle, and it is why a spectrogram of a fast passage looks smeared and a spectrogram of a sustained note looks sharp.
The frequency axis is displayed logarithmically because hearing is logarithmic. On a linear axis the top octave, 10–20 kHz, would occupy half the width while the four octaves containing most musical content would be crushed into a sliver.
Reading the spectrum
| What you see | What it means |
|---|---|
| A sharp spike at 50 or 60 Hz | Mains hum — a ground loop or unshielded cable. 60 Hz in the Americas, 50 Hz elsewhere |
| Spikes at 100/120 Hz and above, evenly spaced | Harmonics of mains hum, typical of a bad power supply or ground loop |
| A broad peak that moves as you walk around | A room mode — a standing wave between parallel surfaces |
| Evenly spaced spikes above a fundamental | The harmonic series of a pitched sound. Spacing equals the fundamental frequency |
| Energy dropping off a cliff around 15–16 kHz | Lossy compression. MP3 and AAC discard the top octave; a sharp shelf is the signature |
| A rising floor across the whole spectrum | Broadband noise — preamp gain too high, or a noisy environment |
| A narrow spike that appears when a fan starts | Mechanical or electrical interference from that device |
About
The Frequency Analyzer displays a live Fast Fourier Transform (FFT) spectrum of the audio captured by your microphone. It is useful for identifying dominant frequencies in a room, checking speaker frequency response, analysing acoustic environments, or just visualising music and voice in real time. The dB range is adjustable to focus on the frequency bands you care about.
How to use
- 1 Click Start Mic and allow microphone access in your browser.
- 2 Play audio, speak, or generate tones — the spectrum updates in real time.
- 3 The peak frequency and level are shown above the spectrum.
- 4 Adjust the dB Min / Max dropdowns to zoom in on the dynamic range.
- 5 Click Stop to release the microphone.
- What is an FFT spectrum analyzer?
- FFT (Fast Fourier Transform) is a mathematical algorithm that decomposes an audio signal into its constituent frequencies. The spectrum analyzer applies FFT to your microphone input in real time and plots the result as a bar graph where the X axis is frequency (20 Hz to 20 kHz) and the Y axis is amplitude in decibels (dB). Peaks in the spectrum show which frequencies are dominant in the sound.
- What practical uses does a frequency analyzer have?
- Common uses include: identifying hum or resonance in a room (often 50 or 60 Hz from electrical interference); checking if a speaker or headphone has a flat frequency response; finding feedback frequencies when setting up a PA system; analysing the harmonic content of musical instruments; and verifying that audio equipment is processing sound as expected.
- What does the dB level on the spectrum mean?
- The dB (decibel) level shows the amplitude of each frequency component relative to full scale (0 dBFS). A value of 0 dB means the signal is at maximum amplitude; -60 dB is very quiet; -120 dB is near the noise floor. Adjusting the dB Min/Max range zooms the display vertically — use a narrower range (e.g. -60 to 0 dB) to see subtle details in loud signals.
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