Online Audio Spectrum Analyzer — Real-Time FFT with Peak Hold & EQ Zones
Analyze microphone input or uploaded audio files with real-time FFT. Features peak hold, EQ zone overlay, dominant note detection, freeze frame, smoothing control, and log/linear frequency scale. 100% browser-based — your audio never leaves your device.
Real-time FFT — 20 Hz to 20 kHz
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What makes this spectrum analyzer different from academo.org and maztr.com
How to use the spectrum analyzer
LazyTools vs other online spectrum analyzers
| Feature | LazyTools | academo.org | maztr.com | checkhearing.org | noisemeter.co |
|---|---|---|---|---|---|
| Peak hold line | ✅ Yes | ❌ No | ❌ No | ❌ No | ✅ Yes |
| EQ zone overlay | ✅ 7 zones | ❌ No | ❌ No | ❌ No | ❌ No |
| Dominant note detection | ✅ Yes | ❌ No | ❌ No | ❌ No | ✅ Yes |
| Freeze frame | ✅ Yes | ❌ No | ❌ No | ❌ No | ✅ Yes |
| Smoothing control | ✅ Slider | ❌ No | ❌ No | ❌ No | ❌ No |
| Log + linear scale | ✅ Both | ✅ Yes | ✅ Both | ❌ No | ✅ Yes |
| Mic + file input | ✅ Both | ✅ Both | ✅ Both | ❌ File only | ✅ Both |
| Multiple display modes | ✅ 3 modes | ❌ Spectrogram | ❌ Spectrogram | ❌ No | ❌ No |
| Cursor frequency readout | ✅ Yes | ❌ No | ❌ No | ❌ No | ❌ No |
| No signup required | ✅ Always | ✅ Yes | ✅ Free tier | ✅ Yes | ✅ Yes |
What each frequency zone means
| Zone | Frequency Range | What it contains | Common problems |
|---|---|---|---|
| Sub Bass | 20–60 Hz | Sub-bass, rumble, room resonances | Muddy mix, speaker overload, inaudible on small speakers |
| Bass | 60–250 Hz | Kick drum, bass guitar, low male voice | Too much: boominess. Too little: thin, weak sound. |
| Low Mid | 250–500 Hz | Body of instruments, vocal warmth | Too much: boxiness, muddiness. Too little: hollow. |
| Mid | 500–2000 Hz | Most vocal content, guitar, snare | Too much: honky, nasal sound. Key for intelligibility. |
| High Mid | 2–4 kHz | Attack, click, presence of instruments | Too much: harsh, ear-fatiguing. Too little: dull, distant. |
| Presence | 4–8 kHz | Sibilance, cymbal attack, vocal air | Too much: harsh S and T sounds. Too little: lifeless. |
| Brilliance | 8–20 kHz | Sparkle, shimmer, very high harmonics | Too much: thin, artificial. Too little: dull, AM radio quality. |
Spectrum Analyzer Guide — FFT, EQ Zones, and Reading the Display
A spectrum analyzer is the audio engineer's most fundamental measurement tool. Where a waveform display shows amplitude versus time, a spectrum analyzer shows amplitude versus frequency — revealing what pitches and tonal qualities are present in a sound at any given moment. This tool uses the Web Audio API's AnalyserNode, which applies a Fast Fourier Transform (FFT) to the incoming audio signal and returns an array of amplitude values across the frequency spectrum.
How FFT analysis works
The FFT size (configurable as 1024, 2048, 4096, or 8192 in this tool) determines the frequency resolution. A 2048-point FFT on a 44,100 Hz signal produces 1024 frequency bins, each representing approximately 21.5 Hz of bandwidth. A larger FFT size gives more frequency bins (better frequency resolution) at the cost of needing more samples before each update (lower time resolution). For general use, 2048 is the sweet spot. For detailed bass analysis, use 4096 or 8192.
Why use logarithmic scale?
Human hearing is logarithmic: each octave is perceived as the same pitch interval. The bass range (20–200 Hz) and the treble range (2,000–20,000 Hz) cover the same number of musical octaves but span very different Hz ranges. A linear display would devote 90% of the width to the treble range above 2 kHz, leaving bass frequencies in a narrow sliver. The logarithmic display allocates equal horizontal space to each octave, making the full frequency range usable.
Online spectrum analyzer free no upload — privacy benefits
Server-based spectrum analyzers like Maztr upload your audio file for server-side processing. This creates delays, file size limits, and privacy concerns. This tool uses the Web Audio API entirely in the browser: microphone access via getUserMedia, file decoding via AudioContext.decodeAudioData(), and FFT computation via AnalyserNode. No audio data is transmitted anywhere. The analysis starts immediately with no loading wait.
Spectrum analyzer — 8 questions answered
A spectrum analyzer displays the frequency content of an audio signal in real time. Horizontal = frequency (20 Hz to 20 kHz), vertical = amplitude in dBFS. Uses FFT to convert time-domain audio into its frequency components.
Fast Fourier Transform: an algorithm converting a time-domain signal (amplitude vs time) into a frequency-domain signal (amplitude vs frequency). Larger FFT size = better frequency resolution but slower response. 2048 is the typical sweet spot.
A secondary line showing the maximum amplitude at each frequency since the last reset. Reveals transient peaks invisible on the live display. Click Reset Peak to clear it.
Sub Bass (20-60 Hz), Bass (60-250 Hz), Low Mid (250-500 Hz), Mid (500-2000 Hz), High Mid (2-4 kHz), Presence (4-8 kHz), Brilliance (8-20 kHz). See the reference table above for what each contains and common problems.
Exponential moving average: high smoothing (90%) = slow, averaged display for sustained levels. Low smoothing (10%) = fast response showing transients. Adjusts AnalyserNode.smoothingTimeConstant in real time.
Pauses the display at the current frame for detailed study. Audio continues to play/listen. Click Freeze again to resume. Useful for capturing a specific moment.
Human hearing is logarithmic. Equal horizontal space per octave makes bass, mid, and treble equally readable. Linear scale devotes most width to treble, compressing bass into a tiny sliver.
LazyTools Spectrum Analyzer is 100% free. No upload, no server, no account, no signup. Mic or file input. Peak hold, EQ zones, note detection, freeze, smoothing. Your audio stays on your device.