Do some research on NRR, and you’ll find that MSA is one of the best in real noise reduction.
SRS tactical has them at 18 db on their website, seems about right based upon my impression from wearing them and several others.
Not sure what you mean by "real" noise reduction unless you are referring to frequency weighting, but my ears and the data I've seen both agree that these are not the best if you are shooting a really loud gun or r.o.ing some shooters shooting open pistols.