How to use it 01 Pick a panel. The five tabs switch instruments; each panel has its own URL. 02 Allow the microphone. Press Start measuring (meter), Start (spectrum, scope) or Start tuning (tuner); the browser prompts for permission. 03 Set up the meter. Choose dB(A) , dB(C) or dB(Z) and set a Calibration dB offset (default 100) matched against a reference meter; read the bar and Min / Max / Leq. Reset stats clears them. 04 Read the spectrum and scope. Spectrum: FFT 2048–16384, log/linear axis, live peak. Scope: 0.1–50 ms/div, FS/div, Auto-scale, Auto / Normal / Single triggering with rise or fall edge, draggable cursors. Capture copies the current window to the workspace with its sample rate. 05 Tune or generate. The tuner tracks single notes and sets A4 from 400 to 480 Hz; the generator plays sine, square, triangle, sawtooth, white or pink noise, with a log frequency slider (1–24000 Hz), a level, and a looped Sweep . Worked examples Rooms and microphones are not reproducible, so the readouts below are deterministic: panel arithmetic plus engine anchors on synthetic spectra.
Panel · input
Readout
SPL meter · 1 kHz tone at −30 dBFS, Calibration 100
70.0 dB(A) on screen; bar yellow (60–85 band)
SPL meter · 40 Hz tone
per-bin weighting: dB(A) −34.5 dB , dB(C) −2.0 dB — 32.6 dB apart
Spectrum · FFT 8192 at 48 kHz
header 48000 Hz · Δf 5.86 Hz ; a peak on the 440 Hz grid reads 439.5 Hz (A4 −2¢)
Spectrum · Capture
mic · 8192 pts @ 48000 Hz ; series capped at 2048 points , floor −160 dB
Scope · 1 ms/div, 0.05 FS/div, cursors T 0.30/0.55 and V 0.35/0.65
Δt 2.500 ms , 1/Δt 400.00 Hz , ΔV 0.1200 FS , T 3.00 / 5.50 ms
Scope · 48 kHz, 32768 samples
header 683 ms window ; a capture reads scope · 32768 pts @ 48000 Hz
Tuner · A4 = 432 Hz, 440 Hz tone
note A4 +31.8¢ ; detected 440.00 Hz ; target 432.00 Hz
Generator · 440 Hz / 82.41 Hz / 20 kHz
note label ≈ A4 / ≈ E2 / blank above ~16.3 kHz
Where the numbers stop
An estimate, not a calibrated measurement. The meter integrates analyser bins from 10 Hz to 20 kHz, skips bins under −140 dBFS and adds Calibration dB (default 100). There is no Fast/Slow/Impulse weighting, no octave bands and no uncertainty budget: trust absolute values only after matching the offset to a real sound-level meter.
Full scale, not volts. Divisions are FS/div because a browser microphone carries no sensitivity data; Vpp, Vrms and mean read in FS, Vrms also in dBFS. The 32768-sample window is 683 ms at 48 kHz; the longest timebase (50 ms/div) fits, and triggering searches that window for the first crossing. What it doesn't do. No WAV recording or file export, no two-channel XY plot (a mono input has no Lissajous meaning) and no speaker calibration. Send captured buffers to Signal Processing , plot the dB series in the graphing calculator , or keep values in the workspace . One room, three decibel scales The dB(A)/dB(C)/dB(Z) switch is not a display preference — it re-weights the spectrum before the calibration offset, and at the low end the scales disagree by tens of decibels:
On the same 40 Hz tone, dB(A) applies −34.5 dB and dB(C) −2.0 dB : 32.6 dB apart . A 20 Hz rumble reads −50.4 dB in dB(A) but −6.2 dB in dB(C).
C is not "A minus something". Around 2 kHz dB(A) adds +1.2 dB above unweighted, and at 10 kHz A (−2.5 dB ) sits about 1.9 dB above C (−4.4 dB ).
Switching the weighting clears Min, Max and Leq on purpose, so frames in different scales never share one average. Measure the same stretch of sound once per scale instead of switching mid-run.
Where it fits Rooms and speakers Pink noise (about −3 dB per octave) or a looped 20 Hz → 20 kHz sweep over 10 seconds shows room modes and speaker roll-off.
Tuning instruments Play one note; autocorrelation suits monophonic sources, the reading turns green within ±5¢ , and frequencies print to 0.01 Hz. Set A4 to 442 Hz for orchestral work or 432 Hz for early music.
Noise at home and in the workshop Leave the meter running and read Min, Max and Leq against the reference table, from 30 dB (whisper) to 120 dB (pain threshold). The bar turns yellow at 60 dB and red at 85 dB — NIOSH's eight-hour exposure limit.
Privacy Microphone audio is analysed in your browser in real time and never uploaded; the generator plays locally; only the calibration and A4 settings are remembered in local storage.
References
IEC, IEC 61672-1:2013, Sound level meters — Part 1 — A, C and Z weighting definitions. webstore.iec.ch （访问日期：2026-10-01）
Wikipedia, A-weighting — 0 dB at 1 kHz, −19.1 dB at 100 Hz, −2.5 dB at 10 kHz. en.wikipedia.org （访问日期：2026-10-01）
Wikipedia, Sound pressure — the 20 µPa reference behind dB SPL. en.wikipedia.org （访问日期：2026-10-01）
MDN Web Docs, AnalyserNode.fftSize — FFT sizes 32–32768, default 2048. developer.mozilla.org （访问日期：2026-10-01）
CDC/NIOSH, About Noise and Hearing Loss — the 85 dBA eight-hour exposure limit. cdc.gov （访问日期：2026-10-01）
Wikipedia, Pitch detection algorithm — autocorrelation for monophonic pitch. en.wikipedia.org （访问日期：2026-10-01）
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Reviewed by CalcX Editorial Team
Updated 2026-10-01