Online Audio Spectrum Analyzer — Freeze Frame & Click-to-Label Frequencies
Analyse the frequency content of any sound in real time via your microphone. Click Freeze to capture a still frame of the spectrum — then click anywhere on the frozen display to label that frequency point with its exact Hz value. Furthermore, Peak Hold mode draws a persistent marker at each frequency's highest recorded level over the session. Choose between bars and line display, logarithmic or linear frequency scale, and export any frozen frame as a PNG image.
How to use the Online Audio Spectrum Analyzer
Click Start Microphone
Click the Start Microphone button and allow microphone access when prompted. Furthermore, the spectrum display begins updating in real time — bars or lines rise and fall as the microphone picks up sound. Play music, speak, or make any sound near the device to see its frequency content.
Choose display settings
Select Bars or Line display style. Furthermore, choose Logarithmic scale for a musical frequency view — this distributes octaves evenly across the display, matching how ears perceive pitch. Linear scale is useful for engineering analysis where equal Hz spacing matters. Enable Peak Hold to show the maximum recorded level for each frequency bin.
Freeze the spectrum
Click Freeze to capture a static snapshot of the current spectrum. Furthermore, the display stops updating and the status bar shows "Frozen." Click Resume to return to live analysis. Freeze is most useful when a specific frequency pattern appears and you want to examine it.
Click to label frequencies
With the spectrum frozen, click anywhere on the display to label that point. Furthermore, a green badge appears showing the exact frequency in Hz or kHz at the click position. Add as many labels as needed. Clear all labels using the Clear Labels button. This feature is unique among free browser spectrum analysers.
Export as PNG
Click Save PNG to download a screenshot of the current canvas — including any frequency labels applied. Furthermore, the exported image is useful for audio documentation, acoustic analysis reports and educational materials. Capture the frozen frame with labels before exporting for the most informative image.
Logarithmic versus linear frequency scale
The frequency scale determines how the horizontal axis is distributed. Furthermore, the choice significantly affects what the spectrum reveals and how useful it is for different purposes.
| Scale | Distribution | Best for | Limitation |
|---|---|---|---|
| Logarithmic | Each octave gets equal space — matches musical intervals | Music analysis, vocal study, instrument tuning, hearing range | High frequencies compressed in the top half |
| Linear | Each Hz increment gets equal space | Engineering, RF analysis, precise frequency measurement | Bass frequencies squeezed into tiny left sliver |
What peak hold mode reveals
Peak hold draws a persistent line at the highest level each frequency bin has reached during the session. Furthermore, it reveals transient peaks that flash too briefly to see in real-time analysis — impact sounds, consonants in speech, and short musical attacks all create brief peaks. Moreover, comparing the real-time spectrum against the peak hold line shows how much headroom exists at each frequency — useful for understanding loudness variation over time.
How frequency spectrum analysis works
The spectrum analyser uses the Fast Fourier Transform (FFT) algorithm to convert a time-domain audio signal into a frequency-domain spectrum. Furthermore, the FFT splits the signal into frequency bins — each bin represents a narrow band of frequencies and shows its current amplitude.
Number of bins = FFT size ÷ 2 = 1024 bins (0 to Nyquist frequency)
Bin N frequency = N × (sample rate ÷ FFT size)
Logarithmic X position = log₁₀(f ÷ 20) ÷ log₁₀(1000) × canvas width
Worked example: analysing a guitar note
A guitarist plays a low E string (82 Hz) near the microphone. The spectrum analyser reveals:
| Frequency | Level | Harmonic |
|---|---|---|
| 82 Hz | High | Fundamental — the note itself |
| 164 Hz | High | 2nd harmonic — one octave above |
| 246 Hz | Medium | 3rd harmonic |
| 328 Hz | Medium | 4th harmonic |
| 410 Hz | Low | 5th harmonic |
What is an audio spectrum analyser?
An audio spectrum analyser displays the frequency content of a sound signal. Furthermore, it shows how much energy is present at each frequency — from the lowest bass to the highest treble — at any given moment. The display updates in real time as the sound changes. Engineers and musicians use spectrum analysers to identify frequency problems, tune instruments, and understand the tonal balance of a mix.
The FFT (Fast Fourier Transform) algorithm powers all modern spectrum analysers. Furthermore, it converts the raw audio waveform — a time-domain signal — into a frequency-domain representation by decomposing it into its constituent sine waves. Each sine wave represents a specific frequency and its amplitude in the analysed signal. Moreover, the browser Web Audio API includes a built-in AnalyserNode that performs the FFT calculation in real time without any additional library.
Harmonics and overtones
Every real-world sound contains a fundamental frequency and a series of harmonics above it. Furthermore, harmonics are integer multiples of the fundamental — a 100 Hz note has harmonics at 200, 300, 400 Hz and so on. The relative levels of these harmonics determine the timbre of the sound — why a violin and a flute playing the same note sound different. Moreover, the spectrum analyser makes these harmonic relationships visible — a skill that acoustic engineers and instrument builders use daily.
Why spectrum analysis matters for audio work
Mixing engineers use spectrum analysis to identify frequency clashes between instruments. Furthermore, when a bass guitar and a kick drum compete in the same frequency range, the spectrum analyser shows the overlap clearly. Cutting one instrument at the competing frequency while boosting the other creates separation in the mix. Moreover, this process — called spectral balancing — is one of the most important skills in professional audio production.
Acoustic engineers analyse room resonances with spectrum analysers. Furthermore, standing waves in poorly treated rooms create frequency buildups that make mixes sound different to other listening environments. Identifying these peaks with a spectrum analyser and treating the room acoustically is the first step in studio acoustic design. Moreover, the freeze frame and click-to-label features make it practical to document room resonances without needing professional measurement software.
Spectrum analysis for voice and speech
Speech coaches and vocalists use spectrum analysers to visualise voice placement and formants. Furthermore, the two main formant frequencies of vowels appear as prominent peaks in the speech spectrum — changing as vowel sounds change. Seeing these peaks while practising vowel sounds gives visual feedback that accelerates vocal training. Moreover, the logarithmic scale is ideal for voice analysis because it spreads the speech frequency range (80–8000 Hz) evenly across the display.
Frequently asked questions
Related music tools
Waveform Visualizer
Visualise audio amplitude over time. Furthermore, export as PNG with color themes for documentation.
Online Tone Generator
Generate pure tones to test the spectrum analyser. Furthermore, binaural beat mode creates two simultaneous frequencies.
Auto BPM Counter
Detect BPM from microphone input. Furthermore, a confidence meter shows the reliability of each reading.
Audio Normalizer
Check peak and RMS levels before spectrum analysis. Furthermore, LUFS presets for streaming are included.
Online Tone Generator
Generate sweep tones to test room acoustics. Furthermore, four waveforms and a note picker keyboard are included.
Guitar Tuner
Tune instruments visible in the spectrum display. Furthermore, 15 alternate tuning presets are included.