Usually within 5 to 10 dB without calibration, and within 1 to 2 dB for everyday sounds once calibrated.
What We Measure
The meter reads the raw signal from your microphone with the browser's voice processing turned off (echo cancellation, noise suppression, and automatic gain). It applies A, C, or Z frequency weighting following the IEC 61672 standard, then Fast (125 ms) or Slow (1 s) time weighting, the same definitions a hardware sound level meter uses. Avg is the equivalent continuous level (Leq) since you started.
Why Phones Differ
Every device has a different microphone and gain, so the same room reads differently on different phones. Some phones also keep adjusting the microphone volume automatically. If that happens, the meter shows a note.
How to Calibrate
Put your phone next to a trusted sound level meter, play a steady sound such as pink noise or a fan, then open Calibrate and Settings and move the slider until the numbers match. The setting is saved on your device, separately for each microphone.
Without a reference meter, use Set Quiet Room in the same panel. Stay quiet for 5 seconds in a quiet room, and the meter sets that room to 35 dB. Quiet rooms are usually 30 to 40 dB, so this is accurate to about 5 dB.
Computer and Webcam Mics
Computer, USB, and webcam mics often read 20 dB or more higher than phones, especially with the system's microphone boost turned on. The meter starts from a lower estimate on computers, and the line under the reading says which calibration it is using. Cheap mics also hiss. In a quiet room they read their own noise, so the meter shows the lowest level your mic can measure.
Limits
- Phone and computer microphones can overload above about 100 to 110 dB, so readings above that will be too low. The meter shows a warning when this happens.
- Bluetooth headset mics filter sound heavily, so their readings are unreliable. Use the built-in mic.
- This is not a certified instrument. For legal or workplace compliance, use a Class 1 or Class 2 meter.
How We Test It
Every release is checked automatically: the filters are compared against the IEC 61672 tolerance table, and a test tone of known level is played through a virtual microphone and must read within 0.5 dB.