Pity it only mentions iOS apps and not the ones I use on Android. I use two apps and they read radically different values (unless I am reading them wrong - that might be the case).
The hardware is at least as important as the software (I'm amazed to see so much scatter between apps), so the homogeneity of the iOS ecosystem is a boon to this sort of measurement. Figure three in their paper shows that the Apple hardware is quite consistent across all models tested.
They did test Android phones and apps; the final paragraph from their results section makes a general statement:
A similar examination of Android apps and devices was not performed because of the low number of apps with similar functionality, and the lack of conformity of fea- tures between devices. Testing conducted with the four Android smartphones also revealed a high variance in measurements of similar apps between different devices.
Thanks for pointing the paragraphs out.
It was a boon to the researchers because it made their job more simple. Given equivalent or better hardware quality, the same measurements could have been taken without regard to which OEM produced the phone; albeit with more effort on the part of the researchers.
I have an app (Sound Meter) which apparently downloads calibration data for a number of popular phone models. This is probably the only realistic solution when you're faced with such a wide variety of hardware. I have no idea how accurate the calibration is though.
It's a byproduct of Apples total ecosystem control that developers have a very good idea of what hardware users have. This has upsides and downsides - with other phone ecosystems you lose accurate sound meters, but you gain a wider variety of devices running the same operating system.
> A total of 62 Android apps were examined and downloaded, however, only 4 apps partially met our criteria and were selected for additional testing.
> Android-based apps lacked the features and functionalities found in iOS apps. This is likely due to the iOS advanced audio capabilities compared to other platforms, the open ecosystem of the Android platform, and having so many different Android device manufacturers using different suppliers and components.