Thanks for that explanationIt is generated from the Android App Spectroid. You can download it and play with it to understand it better. It tells more than just dB.
Original Pro Propeller on MP produces an annoying high pitch sound/ high freq. Sound
Original Platinum Propeller corrected this and shift it to a more bassy sound/low freq.
MasterAirscrew has a better less annoying smooth bassy sound compares to Platinum propeller.
The RPM I got from the RC,l display, I though it was x1000, but somebody corrected, my mistake it is x10. I dont normally measure this, but when the Platinum props hype was high they were asking for this rpm diff.. when MA props have a lower RPM while idling (not hovering), I am sure it still will show that MA has the lowest RPM, following Plat and then Pro.
Your findings on the MA props match what I think I hear ie deeper pitch and your description of them sounding less annoying was exactly what I thought immediately when I fired them up.
When you describe the second type as Original Platinum Propeller - are these the aftermarket DJI ones that they call "Low Noise Quick Release" ?
Also, I forgot there was rpm displayed on the controller - I will have a play comparing DJI low noise with the MA ones as DJI are looser and until we know more about whether the stiffness is an issue they may be a safer bet.