In my experience it's newer buildings that tend to have paper thin walls. In my current apartment(late 70s) I very rarely hear my neighbors.

At my last apartment I could literally hear my neighbors cough. Absolutely miserable. I wish there were some sort of measurable standard rating for noise transmittance through walls that landlords are obligated to disclose to potential renters.

New buildings have strict fire separation requirements that pretty much enforces sound proofing. All new build high rises I have stayed in have had total silence.

Seen many buildings where the concrete walls soundproof the rooms but plumbing ducts in bathrooms transmit sound like crazy - as in you can hear conversations from people several floors down. The inspection hatch cover made of thin sheet metal seems to act like a microphone exciting the air in the duct causing the other covers to act like speakers

It’s really difficult, especially in the bass region. Things like double acoustically isolated walls that are really expensive.

Usually thick insulation because you need mass to block bass.

Like rockwool: https://www.rockwool.com/north-america/products-and-applicat...

Poured concrete, or whatever you might do that is as close to thick, airtight, poured concrete barriers as possible.

Eliminate all holes, and it just becomes a question of mass.

Mass Loaded Vinyl Soundproofing