Acceptable noise buffering levels in walls

CC, The walls separating the apartments are supposed to be fireproof and have sound insulating material. In some condos, separating walls already have two layers of drywall but I do not know industry standard. I would certainly raise it with the developer. Additional layer of drywall is inexpensive if you only have matt or eggshell finish without skim coat. Say 2-3k through a direct worker or super (contractor more). However, the developer should be able to get it done for you. In the worst case, you offer to pay them their cost. And by all means get your neighbor involved too. It will be much better if both sides have extra drywall.

Thanks for the info. So just another layer of drywall would work, no special noise proofing material needed to be added?

No way would merely adding another layer of drywall correct your problem. You need to consult a professional sound-proofing expert. In my coop, I had the same problem as you. In my case, there was about an 8" space between my wall and his wall (concrete with metal lath), and the contractor blew fiberglass foam into the space. It expanded once in and created the equivalent of a cement wall. However, he told me another way would be to build another wall of drywall, but that there would have to be at least 6 to 8" of dead space in order to insulate for sound. Check it out before you go to the expense of adding more drywall only to find out it doesn't do a fig for your problem.

We've had this done twice in two different apartments. The first time in an 80s rental building that the building supplied when we were standing in the bedroom with the building representative deciding if we should rent it and could hear the TV from next door. The second time was in a pre-war that we bought and were renovating. During the renovation we heard a piano. Neighbor's living room to our master bedroom. The rental building had installed three inch studs, soundproofing insulation, then new drywall. We lost about 4" of the room, but it was well worth it. Problem solved, though if you opened the closet door (where there was no soundproofing, you could hear the TV.) The same configuration mostly solved the piano noise, but it was a baby grand (very good classical pianist) in their living room against our bedroom wall. Thankfully they always stopped playing by 9:30 at night.

You can also use this or many other commonly available used with appropriate foam/mud for joints. Also encourage neighbor to use it.

https://www.homedepot.com/p/Gold-Bond-5-8-in-x-4-ft-x-8-ft-Noise-Reducing-Gypsum-Board-50000672/204306334

Some more info. There are several similar products. Marginal cost is just a couple of hundred. Just pick whatever is available at Lowe’s or Homedepot. 10023 solution is superior but you lose 4 inches rather than 5/8 th inch.
https://www.thespruce.com/does-soundproof-drywall-really-work-1821484

You may run up some labor costs in the time required to reset electrical outlets, and reapply baseboard and cornice moldings as well.

Thanks for The Spruce link -- I'll have to think about installing some of the "QuietRock 530 RF" drywall -- I'll be able to take off my tinfoil hat when I'm at home (or line the kids' room with it so they can't play with their cell phone all night).