There's flexibility as a few feet in distance makes a huge difference.
For example, I have a SC-Project Carbon Conic on my Monster 1200R and with the baffle removed it's loud.
However, I was concerned about riding where LEO has road-side sound testing.
I also have a US version Panigale (which is one the loudest stock production bike available).
Therefore, I tried to replicate SAE J2825 and measured the difference both at idle and at 2500 rpm with a decibel meter.
I figure that if the Monster with the SC-P (baffles out) is no louder relative to the Panigale then I would have the high ground in court if it came down to it.
The SC-Project Carbon Conic is no louder (measured) relative to the stock Panigale although it seems louder to the ears.
However and more to the point of distance vs decibels, using SAE J2825 standards (1 [email protected]
degrees), the Panigale measured about 97 at idle and about 102 at 2500rpm. The track marshals measured my Panigale at 93db from 15ft @ 8000rpm.
Distance and other environmental influences such as other bikes nearby will affect the readings. There's flexibility for sure.