About Free Decibel Meter

Free Decibel Meter is a browser-based sound level meter, spectrum analyzer and noise monitor, built to be fast, honest about its own limits, and genuinely free — no account, no app install, no paywalled features.

It's operated independently, from India, as a small side project rather than a company product. There is no sponsorship or affiliation with any hardware manufacturer, standards body, or regulatory agency mentioned on this site.

Methodology

Signal chain

When you start the meter, it requests your microphone's audio stream with automatic gain control, noise suppression and echo cancellation explicitly disabled in the browser's getUserMedia constraints — these voice-call-oriented features would otherwise alter the signal before it's ever measured. That raw stream is processed in an AudioWorklet, a dedicated real-time audio thread separate from the page's main JavaScript thread, so measurement never stutters even if the page itself is busy.

Frequency weighting

A-, C- and Z-weighting filters are implemented as cascaded biquad filters, derived by bilinear transform (with frequency prewarping) from the pole/zero definitions in IEC 61672-1, the international standard for sound level meters. A-weighting, the default, de-emphasizes very low and very high frequencies to approximate how the human ear perceives loudness at moderate levels; C-weighting is closer to flat and better suited to peak/impulse measurements; Z-weighting applies no frequency shaping at all.

Time weighting

Fast and Slow response follow the same exponential time-averaging time constants IEC 61672-1 defines: 125 ms for Fast, 1 second for Slow. Leq, in contrast, is a true linear energy average over the whole session, computed from the sum of squared instantaneous levels rather than either exponential average — which is why a brief loud spike can move it more than an equally brief quiet moment moves it back.

Calibration

By default, the tool applies a generic offset intended to bring typical consumer microphones into a broadly plausible range — it is not a measurement of your specific device. For a meaningfully accurate reading, use the calibration option in Settings to enter a reading from a trusted reference sound level meter taken at the same moment and location; the tool computes and remembers an offset for that specific microphone going forward.

Known limits

This is not a substitute for a calibrated Class 1 or Class 2 sound level meter built to IEC 61672-1 or ANSI/ASA S1.4, and it should not be used for legal, regulatory, or occupational-compliance measurements. Consumer microphones vary in sensitivity and frequency response between devices, some mobile browsers apply audio processing that cannot be fully disabled from a web page, and no software correction can fully compensate for that. Typical accuracy, uncalibrated, is within roughly ±3–5 dB of a reference meter under normal conditions.

Editorial policy and corrections

Every specific figure on this site — exposure limits, regulatory thresholds, example sound levels — is drawn from a named, linked source (see the Sources section on each page) rather than invented or approximated without attribution. Where a figure is a typical/representative value rather than a precise constant (most real-world example sounds), that is stated explicitly.

If you believe something on this site is inaccurate or out of date, please get in touch via the Contact page — corrections are welcome and will be made promptly once verified.