More like -39db, with is about an average rating for a rifle suppressor (Gemtech, Surefire, AWC, et al.).
For a rifle, it makes the sound bearable without ear protection, but nowhere close to silent. I was interested in a Gemtech Halo suppressor, but it doesn’t do enough for me.
Now, you can suppress a round integrally by slowing down the round and bleeding off/moderating gas along the entire length of the barrel. An integral .22 is about as quite as an airgun with the right ammo.
Watch the linked video: you’ll shit a brick at how quiet it is.