How do I compare dB apps?
Many apps in the App Store measure sound level in dB. What is the difference between them?
The Importance of Calibration
The calculation of relative sound level in dB is quite straightforward, and we can hope all app developers have implemented this correctly. However, the calculation of absolute sound pressure level (SPL) requires calibration of the system. Many factors affect calibration. Some of these such as device type and model can be accounted for by the app developer (if they have done a good job). Others such as component batch and ambient temperature cannot. This means that even if the app is only to be used to monitor environmental sound levels, calibration is a good idea.
For voice measurement, calibration becomes imperative because the position of the recording device relative to the mouth varies according to user preference. Voice norms for SPL are typically standardized at a fixed mouth-to-microphone distance of about 30 cm. So if the iPhone or iPad microphone is not pointed at the mouth from 30 cm away, then even an app that is "pre-calibrated" by the vendor will measure an incorrect value. The difference in measured values between an iPhone held up to the mouth and one held at arms-length can be 18 dB. For this reason, Sonneta Voice Monitor provides a voice-activated calibration function to allow you to easily calibrate the system in whatever position works best for the user.
The iPhone contains multiple microphones with adjustable gains. It is important when making measurements to ensure that only the main microphone is used with a fixed gain setting. It is also important to track when a headset or external microphone is plugged in, since the calibration will change. All of these things are the app developer's responsibility to get right, or the measurement will be nonsense. Sonneta Voice Monitor accounts for these and many other details to give you a reliable measurement tool you can trust.
Things to Check
- Can the system be calibrated in the position in which it will be used?
- Does the developer show an awareness of sound measurement issues and pitfalls (so that you can trust their app)?