There are exceptions to every generalization, and this exception is pretty cool. The Welrod MkIIA is a semiautomatic pistol, designed for covert operations and assassinations, that is genuinely movie-quiet.
Ian McCollum (Forgotten Weapons) has an excellent video:
"When it's properly set up, this is as close as you get to an actual `silent gun`. You can, by all accounts, be within about 15 feet of this thing and not recognize that a firearm has discharged."
Note that it's still 122dB. That's quiet for a firearm, which is normally 140dB or more, but still louder than a car horn.
I think the proper way to read the quote is that you'll definitely hear the sound, but it won't necessarily be obvious that it has come from a firearm.
Wikipedia says 122db, but I don't think that's correct. Other sources say 73db, and describe the sound as less loud than that of the bullet impacting the woid of the target, at least with fresh baffles. (Too lazy to include links, first page google results)
You can’t tell the SPL from a YouTube video but you can clearly tell the silencer reduces the attack and sustain of the gunshot noise by a substantial degree. It also doesn’t echo as much.
Ian McCollum (Forgotten Weapons) has an excellent video:
https://www.youtube.com/watch?v=d12AjvEsaHg
"When it's properly set up, this is as close as you get to an actual `silent gun`. You can, by all accounts, be within about 15 feet of this thing and not recognize that a firearm has discharged."