Guides

How to calibrate your phone as a sound meter

Put your phone next to a reference sound level meter, play a steady noise, read both in dB(A), and set your app's calibration offset to the difference. Check it at a second, louder level. Without a reference meter, leave the offset at zero: guessing from "a quiet room should be 30 dB" makes readings worse, not better.

Why phones read differently

• Microphones vary. Android requires a known sensitivity for the raw microphone input, but real phones still differ by a few decibels.
• Audio processing. Phones clean up sound for calls with automatic gain and noise suppression. A good meter app asks for the unprocessed input where the phone offers it, and the voice-recognition input otherwise, which has gain control off.
• Cases and position. A case over the microphone hole, or holding the phone with your hand over it, can easily cost several decibels.
• Loud sounds. Phone microphones are built for speech. Many compress or clip above about 100 dB, so readings there are often too low, and calibration can't fix that.

Calibrating against a reference meter

1. Borrow or buy a meter you trust: a Class 1 or Class 2 meter is best. Schools, music shops, makerspaces and audio-engineer friends often have one.
2. Use a steady, broadband sound: a fan, a running tap, or pink noise from a speaker. Avoid music and speech, which jump around.
3. Aim for a moderate level, about 65–75 dB(A), well above the room's background and well below where phones struggle.
4. Place both microphones side by side, the same distance from the source and pointing the same way. On most phones the microphone is a small hole on the bottom edge. Take the case off.
5. Match settings: dB(A) and Slow response on both.
6. Wait 10–20 seconds, then compare the averages, not a single moment.
7. Set the offset to reference minus phone. If the meter shows 72.0 and the phone 69.5, set +2.5 dB.
8. Check a second level, 10–15 dB louder or quieter. If both agree within about 1 dB, you're done. If not, use the offset that fits the level you measure most.

No reference meter?

• Leave the offset at zero and compare relative levels: before and after, room to room, night to night. The differences are reliable even when the absolute number is off by a couple of decibels.
• Don't calibrate against "known" levels from tables. A "60 dB conversation" can be anywhere from 55 to 70.
• Note in your diary or report that the phone wasn't calibrated.

External microphones

A USB or headset microphone has its own sensitivity, so calibrate it separately and keep a separate offset for each microphone. Measurement microphones with a USB interface can be checked with an acoustic calibrator (94 dB at 1 kHz) if you have one.

Phone microphones aren't certified sound level meters. Readings are estimates; see our terms.