EDITED 21 April. I've discovered a source for how motorcycle noise is measured in Europe. It's EEC Directive 78/1015/EEC. The test, essentially, is to accelerate the bike over a 20m distance in second or third gear between two microphones 15m apart. I found a research paper that compared the results of the European Union test with a static test. It's here. In short, the static test produced sound pressure levels that were up to 13dB(A) higher than the EU drive-by test, with almost all results falling within two standard deviations of the drive-by mean. A factory standard Honda Fireblade produced 83dB(A) in the drive-by test and 95dB(A) in the static. That's equivalent to 83dB(A) at 2m.
Kerbside of busy road 88dB(A)
Oh, and lest we forget, these are maximum noise levels. If you don’t ride around at maximum, wide-open throttle, your machine will be a lot quieter. Everyone, surely, owes it to common decency to keep the noise down when leaving at the crack of sparrowfart or getting home after a session of midnight oiling.
Stock muffler 98dB(A) (the EPA limit, measured at 2 metres)