How the meter works

1. Acquire audio with permission

The meter opens an audio-only stream after an explicit button press. It requests one channel and asks the browser to disable echo cancellation, noise suppression and automatic gain where supported. The track settings are checked for reported processing. The app does not monitor audio through your speakers.

2. Apply approximate digital A-weighting

Three second-order IIR sections are derived from the analog A-weighting pole frequencies 20.598997, 107.65265, 737.86223 and 12194.217 Hz using a bilinear transform. The digital response is normalized at 1 kHz. This is an approximation, particularly near the upper end of the audio band, and does not certify the system to IEC 61672.

The analog filter model is described by Rimell, Mansfield and Paddan, “Design of Digital Filters for Frequency Weightings (A and C) Required for Risk Assessments of Workers Exposed to Noise”, Industrial Health (2015). The implementation is independently written.

3. Accumulate non-overlapping audio windows

An AudioWorklet continuously sums squared weighted samples in 125 ms windows. Digital level is 10 × log10(mean square), with a numerical floor of −140 dBFS. The live reading and minimum/maximum describe these windows. They are not true instantaneous acoustic peaks and do not implement a certified Fast or Slow exponential time response.

The session average is 10 × log10(total energy / captured duration), plus the offset. It is not an arithmetic mean of decibels. This is an energy-equivalent calculation, not a validated acoustic LAeq instrument. The final incomplete window, up to 125 ms, is omitted when you stop.

4. Show two different charts

The history displays the final 30 seconds of captured A-weighted estimates. Its visible vertical range is 0–130 dB; values outside that range are clipped on the plot only, not in statistics or exports. Before 30 seconds have accumulated, the horizontal scale fills from the left.

The spectrum comes from an unweighted 2048-point browser analyser. Bars show the strongest FFT bin in each logarithmic band from 60 Hz to the lower of 16 kHz and Nyquist. Its units are digital dBFS, not calibrated acoustic dBA.

5. Keep processing local and bounded

Audio samples are not recorded or uploaded. Memory holds summary statistics, the recent history and 1-second energy summaries for CSV. Sessions stop at six hours. Backgrounding the page or an audio interruption stops the run; restarting begins a new session. Download any result you want to keep before starting again or reloading.

The report includes the final chart snapshots and whole-session statistics. A user-applied alignment is documented and affects the entire session. Only alignment is saved in browser storage; the measurement history and report notes are not persisted.

Exposure calculator

For a manually entered level from 70–130 dBA, the calculator evaluates T = 8 × 2^((85 − L) / 3) hours. Results above 24 hours are labelled accordingly, not as unlimited exposure. This is an illustration of the NIOSH occupational 3 dB exchange-rate reference. It does not use or validate your browser reading, measure cumulative daily dose or establish personal safety.