Well, understanding how it does it isn't easy, that's for sure.
But why is simple enough. You think of "volume" as apart of a sound. While a computer's hardware essentially doesn't. A sound is just varying wave lengths. Brstrms hence don't consider the variable "volume" as
humans like to as it only considers a more "base" data type (think of people using binary over other forms of numbers).
Mp3 "Sound": A[50 volume]B[49 volume]C[99 volume]DE etc
brstrm "sound": LALALALALALALALALALAAAAAAAAAAAAAAAAA~ and then the game figures out how loud that laaaa is based off the entirety of the file.
I could probably equate 30% of my daily problems trying to explain to people (my family) how crappy human standards are when working within the realms of computational logic