my understanding is that sound transfer mitigation is dependant on the build of the building (wood vs concrete) and the noises (high freq/low freq). It's all in the joint assembly detail and materials used to specifically mitigate sound transmission (and flanking).
You can't use the same material the same way in a wood frame vs a concrete building - they behave differently. You can spend a lot of money thinking you're doing something with little to no results if not designed properly, and the opposite with a good detail/design.
Then you get in to what most people probably hear, impact noises from contact with the floor (i.e. hamster upstairs playing a game of full court basketball)...i.e. IIC as noted above.
all this stuff is over my head, i just look at STC/ASTC ratings and let people smarter than me figure it out
