Decibel meter with A, C and Z weighting and a calibration offset

A sound level meter that takes the physics seriously — proper A, C and Z weighting, a time constant, and a calibration offset so your phone can be matched against a real meter.

Why most phone decibel apps read too high

A phone microphone can measure sound level reasonably well, but two things routinely go wrong. The first is weighting: if an app reports the raw, unweighted level, low-frequency rumble that human ears barely perceive inflates the number, sometimes by fifteen or twenty decibels against a meter using A-weighting. The second is calibration: every phone model has a different microphone response, and without an offset the reading is a good relative measure but a poor absolute one.

This app addresses both explicitly. You choose the weighting curve, and you can dial in a calibration offset in decibels to align the reading with a reference meter.

What it measures

The main screen is a gauge and three statistics; the depth is in Settings.

• A, C or Z frequency weighting. A-weighting matches human hearing and is the standard for noise exposure — it is what workplace limits are quoted in. C-weighting is nearly flat and is used for peak and low-frequency work. Z is unweighted, raw and unfiltered. The app explains each one in place, and the unit label changes to dB(A), dB(C) or dB(Z) so you always know which you are reading.
• Time weighting. Fast and slow time constants change how quickly the reading responds. Slow smooths out transients for an ambient level; fast catches short events.
• Minimum, average and maximum. A single instantaneous number is nearly useless for characterising a space. MIN, AVG and MAX over the measurement window tell you whether a room is steadily loud or occasionally loud, which are different problems.
• Peak history. Peaks are saved so you can review them later, with an undo when you clear the list.
• A calibration offset. Set an offset in decibels, adjustable in tenths, to align your phone against a calibrated meter or a known reference. There is a reset to zero if you want to start again.
• A device report. The device report screen shows what the app is getting from the audio hardware — useful when a reading looks implausible and you want to know whether the phone or the app is responsible.

Honest about what a phone can and cannot do

A phone is not a Class 1 sound level meter and this app does not claim to be one. Microphones on consumer devices have limited dynamic range, they compress at high levels, and their frequency response varies by model. What a well-built phone app can do is give you a consistent, weighted, calibratable reading — good enough to tell whether a café is 65 dB or 85 dB, and good enough to document a noise problem over time.

The measurement runs entirely on the device. Audio is analysed in memory and never recorded to a file or transmitted; the microphone is only active while you are measuring.

What people measure with it

Home noise disputes are the most common use — documenting how loud a neighbour's music or a nearby construction site actually is, with a timestamped peak history rather than an adjective, which is a far stronger position when you raise it with a landlord or council.

Workplace curiosity is second: checking whether an open-plan office, a workshop or a bar is in the range where hearing protection starts to matter. Musicians and audio people use it to sanity-check rehearsal room levels. And parents use it to check a toy, a nursery or a cinema screening before deciding whether small ears need protecting.

Accuracy and privacy

Readings depend on your device's microphone. For absolute accuracy, set the calibration offset against a known reference; without calibration, treat the numbers as consistent relative measurements. A-weighting is the setting to use if you are comparing against published noise-exposure limits.

The microphone is used only while measuring. No audio is recorded, saved or uploaded — only the computed level. The app is free and ad-supported.

Frequently asked questions

What is the difference between dB(A), dB(C) and dB(Z)? A-weighting matches how human hearing responds and is the standard for noise-exposure limits. C-weighting is nearly flat, used for peak and low-frequency work. Z is unweighted — the raw level, no filtering.

Why does my phone read differently from a real sound level meter? Microphone response varies by device. Use the calibration offset in Settings to align your phone against a reference meter; it adjusts in tenths of a decibel and can be reset to zero.

Does it record what it hears? No. Audio is analysed in memory to compute the level and is never written to a file or transmitted. The microphone is active only while measuring.

Does it need an internet connection? No. All measurement and analysis happens on the device.

Is it accurate enough for legal or workplace use? No. A phone is not a Class 1 or Class 2 sound level meter. It is good for indication, documentation and comparison — not for regulatory measurement.