Decibel Meter

This meter listens to your microphone and turns the signal into a sound level reading. It takes the raw waveform many times a second, computes the root mean square of each block — the energy in that slice of sound rather than any single sample — and converts that to a logarithmic scale, because loudness is perceived logarithmically. A sound ten times more powerful reads as roughly ten decibels higher, not ten times higher.

The part a browser cannot do on its own is the final step. Web audio reports level relative to digital full scale, which says how close the signal is to clipping but nothing about the sound pressure that produced it. Bridging the two requires knowing the microphone's sensitivity in volts per pascal, and no browser exposes that. The calibration offset stands in for it: it shifts the whole scale up or down, so if you set it against a meter you trust once, every later reading on that device becomes useful.

Three things work against accuracy on consumer hardware, and all of them push in the same direction. Laptop and phone microphones are tuned for speech, so they roll off the low frequencies that dominate traffic and machinery noise. Automatic gain control quietly adjusts sensitivity, which flattens exactly the steady background you are trying to measure. And loud sound is compressed rather than reproduced faithfully, so peaks read lower than they are. The practical consequence is that relative comparisons on one device are far more trustworthy than any absolute number.

Used within those limits it answers real questions. Is the bedroom quieter with the window shut. Is the new fan actually louder than the old one. Does the workshop cross into the range where prolonged exposure matters — occupational guidance generally treats 85 dB sustained across a working day as that threshold, with the tolerable duration roughly halving for every 3 dB above it. For anything with legal or medical weight, a calibrated meter is the only defensible instrument.

The microphone stream never leaves your browser. Nothing is recorded, stored, or uploaded, and stopping the meter releases the microphone immediately.