New Jersey is one of the states that does not permit the ownership of removable sound suppressors. The state legislature has "explicity banned" silencers.
Well they are legal and you know what it depends on how much noise you are making. If there is no question that the level of sound coming from your building interferes with the work and play of others then you will face the court of a sound suppressor for sure.
You have to be careful here, if you are referring to firearms. This may be legal,in parts of New Jersey, but forbidden or proscribed by federal law or local statute.