dB Toolkit — Support

Point the top of the phone at what you are measuring. The app measures through the microphone next to the front camera, and that is the one the calibration was derived through. Hold it away from your body — a hand over the microphone is worth several decibels, and always in the direction of reading low.

Longer than feels necessary. A glance at the dial tells you almost nothing about an intermittent noise. For a neighbour dispute, record the whole episode: the useful evidence is when it happened and for how long, not the loudest instant.

Yes, if you can. Almost every assessment — BS 4142 especially — is about the difference between a sound and the background it sits in, not the sound alone.

Every microphone has a noise floor of its own, and a phone's is not published. Very low readings are likely to be measuring the microphone rather than the room, so treat the bottom of the scale as a limit of the instrument rather than a measurement of silence.

The app ships a constant measured by substitution against a calibrated reference microphone, and every report states the uncertainty that comes with it — about five decibels on the iPhone it was measured on, six or seven as an estimate for others. Where the app cannot be sure, it says so rather than rounding the doubt away.

No. It is a phone. It has not been type-approved and cannot be verified with an acoustic calibrator, because a calibrator couples to a half-inch microphone body and will not couple to a phone. For a measurement that has to stand up on its own in court or in a formal enforcement action you need a calibrated instrument and somebody qualified to use it. What this gives you is a competent, honest, timestamped record.

Yes. A calibrated USB microphone — a Dayton iMM-6C, a miniDSP UMIK — will measure properly. Plug it in, then go to Settings → Calibration → Microphone and either import its calibration file or type the sensitivity from it. Use the file for your own serial number, never the datasheet: the iMM-6C used to calibrate this app reads 1.3 dB away from its own model specification.

No. The phone-only path is fully calibrated. The honest answer to "is this accurate?" is never "buy hardware".

The date and times, the duration, which microphone was used and which end of the phone it was, what the scale is referenced to and its uncertainty, the location if one was captured, the level graph with the audio waveform, the statistics, the loud events with their times, the noise exposure, and any verdict against a limit you selected.

Because it is. A phone measures on a scale carrying a stated uncertainty of five to seven decibels, so a reading of 86 dB against an 85 dB limit is not a pass and it is not a fail. A confident tick there would be a made-up certainty in a document you might act on. For a reading that close, a calibrated Class 1 or Class 2 instrument is the way to settle it.

Yes. With Pro, CSV export contains every reading with its timestamp, so you can check the app's working and your data is never held hostage.