10000% effective for me in order to sleep. I live in a loud neighborhood with very rude neighbors who play loud bass. Brown noise (albeit cranked very loudly via a Lectrofan brand machine) keeps low frequency nuisance at bay. It can't block out the physical aspects of loud upstairs neighbors stomping or loud cars rumbling past, but it has really saved my sanity and blocked 90% of the noise.

White noise on the other hand doesn't really do it as much for me, but is helpful for blocking out people talking, higher frequency sounds, etc.