Frequency Analyzer: Reading the Live Spectrum

What the spectrum shows

The spectrum panel breaks live microphone input into frequency bands and draws their energy as bars: low bass on the left, speech mids in the centre, treble hiss on the right. Taller bars mean more energy at that pitch. Switch the meter visualisation between Level for the instant dB value, Waveform for the raw signal shape, and Spectrum for this frequency view — all three update live while measuring. Measurement itself never uses these display bars; levels come from the time-domain engine described in how measurement works.

When analysis beats a single number

• Music and speakers: see bass, mids and highs at a glance instead of guessing from one dB value.
• Voice recording: spot mains hum, room resonance or harsh hiss before recording.
• Neighbour and traffic noise: tell low rumble that vibrates walls apart from mid-range speech and high brake hiss.
• Weighting checks: compare A-weighting against C-weighting on bass-heavy sound — dB vs dBA explains why the two diverge.

How to run it

1. Open the meter and allow microphone access, as in how to use.
2. Select the Spectrum tab in the visualisation card.
3. Play or await the sound — music, voice or room noise — and watch the bars react in real time.
4. Flip to Waveform to inspect clipping or dropouts, or back to Level for the dB readout and Leq.

Reading the picture honestly

Phone and laptop microphones favour the speech range, so very low bass reads lower than it sounds and the spectrum is a visual reference, not lab analysis. A dominant left edge means rumble from traffic or ventilation; a strong centre means speech or TV; a raised right edge means hiss from electronics or escaping steam. For certified acoustic work you still need lab-grade hardware — see accuracy and limitations. For level context, continue with the decibel comparison chart and noise exposure.

Set timing before you trust shapes

Grant microphone permission over HTTPS, then let the meter settle for 30 to 60 seconds before you judge any hump permanent. Fast at 125 ms sketches every syllable as a jumping bar, while Slow at 1 s irons those jolts into a readable trend. Your A, C or Z choice follows the dominant band, so flipping from A to C on a bassy idle visibly lifts the left edge. Ignore single-decimal flicker, since phone models commonly spread 5 to 10 dB apart on identical noise.

Three room stories the bars tell apart

• Night bus outside: a thick left wall below speech, centre nearly flat, right edge asleep — you feel pressure more than you hear detail.
• Kitchen kettle filling: centre speech dips for two seconds, then the far right climbs as steam hisses near 6 to 8 kHz.

Hold a phone a metre from television dialogue. Centre bars dance with vowels while the left stays low. Carry the same phone to an open window facing traffic and the picture inverts: left surges with rumble. That contrast shows whether closing the window treats the intruder, and the decibel comparison chart puts numbers beside those shapes.

Pair the view with Leq instead of chasing peaks

Peaks seduce you. A single clap can spike the instant value while the room average barely moves, which is why the meter keeps current, minimum, Leq, maximum and duration side by side with a 240-point history graph. Watch Spectrum for character, glance at Leq for dose: a 45-second passage averaging near 62 dBA tells you more than three startling 78 dBA peaks from cutlery. When the Waveform flattens near 95 to 100 dBA, treat the view as clipped and back the source down. Sounds below roughly 30 dBA sink toward the microphone floor too.

Play a known pitch from the tone generator in a second tab at modest volume and you will see a narrow tower slide as you drag from 220 Hz to 4 kHz. For method background see how measurement works and how to use the meter.

Where the browser view runs out

Your display bars never feed the level engine, they only illustrate it, and phone capsules under-report deep bass by design. Formal surveys still demand Class 1 or 2 hardware — this page gives screening insight for everyday choices like microphone placement or whether to shut a door. The page holds up to 20 recent sessions in your browser, exports dB tables only after a device-specific offset against a known reference, and records usage counts without ever receiving audio. Re-read accuracy and limitations before quoting any figure elsewhere.

Open the online decibel meter → · What a sound level meter is →