Environmental Noise Monitor
This environmental noise monitor works as a free noise monitoring app in your browser, continuously tracking the live noise level around you from your microphone. A big live readout, a scrolling time-series chart, and running Min, Max, Leq (equivalent continuous level) and L90 (background) statistics — plus a settable alert threshold that flashes when the level is exceeded.
ℹ This is an uncalibrated, relative estimate — not a certified sound-level meter. A browser mic can’t know its real-world sensitivity, so the tool reads dBFS (relative to digital full scale, always ≤ 0). It shows an estimated dB SPL only if you calibrate it against a real meter (shared across every noise tool). It is not valid as legal, complaint, or compliance evidence — for that use a calibrated Type 1/2 meter. The tool requests auto-gain, noise-suppression and echo-cancellation be turned off (a reading is meaningless otherwise); most browsers honor this but the OS audio stack can override it. Nothing is recorded or uploaded.
Microphone
Audio is analysed live in your browser to compute the level. It is never recorded, saved, or transmitted.
Alert threshold
Compared in dBFS (the same scale as the big readout, the stats and the chart), so it stays consistent whether or not you calibrate. Visual only — no sound is played.
Live level
Scrolling level history (newest on the right). The red dashed line marks your alert threshold.
Calibration (optional, shared across all noise tools)
To estimate dB SPL, start monitoring, read the level on a real sound-level meter or a calibrated phone app at the same spot, type that number below, and press Set. The offset is stored locally and reused by every Noise Analysis tool — calibrate once. It remains an uncalibrated estimate, not a certified measurement.
How It Works
When you press Start, the tool requests microphone access with automatic gain control, noise suppression and echo cancellation turned off. Those processors constantly change the signal’s level to "improve" speech, which would corrupt any noise measurement — so the tool asks the browser to disable them; if your system still applies processing you cannot fully disable, treat the readings with extra caution.
Each animation frame, the raw time-domain samples are read from a Web Audio AnalyserNode. The tool removes any DC offset, computes the RMS (root-mean-square) energy of the frame, and converts it to dBFS — decibels relative to digital full scale, where 0 dBFS is the loudest signal the system can capture and everything quieter is negative. A short integration time constant (~125 ms, like a meter’s "fast" response) smooths the reading so it tracks perceived loudness without flickering.
Four times a second a level point is recorded. The sound level chart draws a bounded scrolling history (older points fall off the left), while the running statistics below cover the whole session so all four describe the same time span:
- Min / Max — the quietest and loudest smoothed levels seen this session.
- Leq — the equivalent continuous level over the session:
10·log₁₀(mean of 10^(L/10)), i.e. the steady level carrying the same total energy as the varying sound. - L90 — the level exceeded 90% of the time over the session, the standard proxy for the background (residual) noise.
These are computed from the uncalibrated dBFS levels recorded over the whole session, so they are valid as relative metrics — perfect for comparing before/after with the same mic and setup, or for watching how a level drifts over a session. If you calibrate against a real meter, the tool adds your offset to show an estimated dB SPL; the offset is shared (via your browser’s local storage) with every other tool in this category, so you only calibrate once.
What it cannot do honestly: give you a certified absolute dB SPL, serve as legal or compliance evidence, or capture true infrasound — consumer mics roll off sharply below about 20 Hz and at the very top of the spectrum. The alert threshold is a number you set yourself; the tool simply flashes when the relative level reaches it. It is not compared against any published noise standard (such as WHO or OSHA/NIOSH limits).
A related distinction worth understanding: environmental meters typically apply A-weighting (the dBA scale) to match human hearing sensitivity, which de-emphasises very low and very high frequencies. This tool measures a flat (unweighted) broadband level — it treats all frequencies equally. The difference is usually small in ordinary indoor or traffic environments but can be significant for machinery with strong low-frequency content. If you need to assess against a guideline that cites dBA (most WHO and OSHA thresholds do), a calibrated dB SPL meter with A-weighting is the appropriate instrument. For a longer-term noise diary rather than a live session, the noise level logger can accumulate data across an extended monitoring window.
dBFS vs dB SPL vs dBA: Which Decibels Is This?
dBFS (decibels relative to digital full scale) is what this tool reads from your browser microphone. It is a relative digital scale: 0 dBFS is the loudest signal the audio system can represent, and everything quieter is a negative number. Because it depends on your microphone's unknown sensitivity and your OS gain settings, dBFS alone tells you nothing about real-world loudness — it is only meaningful for comparing before-and-after changes with the same mic setup. dB SPL (sound pressure level) is the physical scale, referenced to 20 micropascals (the threshold of human hearing). Expressing SPL requires a calibrated transducer; a browser cannot determine this on its own, which is why this tool offers an optional manual calibration offset rather than claiming to read SPL directly.
dBA is A-weighted dB SPL: the signal is filtered to de-emphasise very low and very high frequencies that humans perceive as less loud, making the reading correlate better with perceived noise. OSHA, NIOSH, and most environmental noise ordinances specify limits in dBA precisely because it reflects human exposure — not raw sound energy. This tool measures a flat, unweighted broadband level (not A-weighted), so its readings are not equivalent to dBA even after calibration. If your goal is to check against an occupational or community noise limit, you need a calibrated meter with A-weighting enabled. The noise exposure calculator explains OSHA/NIOSH dose thresholds in more detail, and the sound pressure level calculator shows how SPL, distance, and reference levels relate mathematically.