cafeIKE wrote:As a retired sound engineer, smartphone apps are somewhat suspect unless they are calibrated.
Very few places today have a 30dB ambient noise level. 50 is pretty darned quiet.

For sure. I did it more for my own entertainment. But subjectively, they order about like the numbers suggest.

This follow-up study suggests that using external, calibrated, microphones greatly improves the overall accuracy and precision of smartphone sound measurements, and removes much of the variability and limitations associated with the built-in smartphone microphones.

from CDC NIOSH Science Blog: So How Accurate Are These Smartphone Sound Measurement Apps?

In the 5 years since the standalone calibrated update, I've not found any difference to their findings.

It is possible to calibrate the internal microphone for close enough, but it requires an external calibrated mic, a reference level generator and a known signal source.

I have a Kafatek MC3 and a Niche. For me the Kafatek is much better. Good coffee prep isn't that easy and takes years and lighter roasts can be much harder to get right. At the end of the day only a good barista can really test the potential of a grinder, much like I couldn't tell you how good a given Ferrari was compared to a BMW; I am just not a good enough driver! If you go to the Kafatek forum you will see that if you are using the Max, by way of example, possibly the best grinder out there, your shots might be far worse than with a lesser grinder, as your prep might not be up to it. A good video to look at is the following one from Decent, http://www.youtube.com/watch?v=xZFMKBG5sp4 where you can hear how easy is it is to mess up a shot; I know it talks about roast level, but in that there is quite a bit about prep and the pluses and minuses of different profiles.