Online sound level meter

I tried a bunch of online sound meters and noticed something odd - my readings were always lower than what my phone's built-in meter showed. Turns out, browsers apply three layers of audio processing by default: automatic gain control (compresses loud sounds down), noise suppression (removes what it thinks is background noise), and echo cancellation. These are great for voice calls. They're terrible for measurement.

With AGC on, a 75 dB room and a 55 dB room can show nearly identical readings because the browser is normalizing everything toward "comfortable speech level." You're not measuring the room anymore - you're measuring the browser's opinion of what the room should sound like.

This tool explicitly requests that all three processors be disabled via the getUserMedia constraints API. Not every browser fully respects this - Chrome does reliably, Firefox mostly does, Safari is inconsistent. But even partial compliance gives you something closer to the truth than the default.

That's it. That's the whole reason this exists. One problem, one fix.

The meter lets you switch between three frequency weightings. They change how much each part of the sound spectrum counts toward the final number, following the curves defined in IEC 61672, the international standard for sound level meters.

• dBA (A-weighting) - matches how the human ear actually perceives loudness, quietening the very low and very high frequencies we are less sensitive to. This is what almost every noise regulation and hearing-safety guideline uses, so it is the right default for checking rooms, offices and workplaces.
• dBC (C-weighting) - stays flat across most of the audible range and keeps far more bass. Use it for music, concerts, home theatre and anything with strong low-frequency content, where A-weighting would understate the real level.
• dBZ (Z-weighting) - zero weighting, the raw unfiltered level. Useful when you want the untouched measurement with no perceptual curve applied.

If you own a calibrated meter, hold it next to your device in a steady sound and use the Calibrate buttons to nudge the reading until the two match. That offset is saved in your browser for next time.