[asfeir]

Any physical phenomena perceived by our senses, is subject to very complex physiological laws. As photographers we know well (do we really??) all the issues of color, color temperature, etc...

Sound is no different! It is well known that 3dB is the minimum difference of sound that can be detected by human ears. That might be slightly different for impulse sound like that of a shutter. Sound level perception is usually measured in Phones not dB (there is a complex relation between the 2)

This said, perception will depend on the frequency content, duration of the impulse, etc.

Comparing recorded sounds adds more complexity (frequency response of the mic, the speakers, etc.)

I did listen to M8 and M8.2, the M82. is perceived as much quieter