I came across the article on "House & Home", not too informative but I always like to point my readers to any new articles that discuss soundproofing. One product is mentioned in this article which is db-Bloc.
"Sound transmission between units is one of the biggest complaints among condo dwellers today. Moving from a single-family home, many condo owners aren’t used to sharing common walls with their neighbors.
Although some noise in shared living spaces is normal, if you can clearly hear your neighbors’ conversations, you have a noise problem, said Eric Wolfram, lead acoustical engineer for Riedel & Associates, an acoustical consulting firm in downtown Milwaukee.
Wolfram explained that the state building code only requires condos to meet an STC (sound transmission class) of 45, which means that normal conversation levels between units will be muffled, not inaudible. In other parts of the country, building codes now require condos to meet an STC of 50, while luxury developments might aspire to an STC of 60 or higher.
“We get calls from a lot of disappointed people,” Wolfram said. “They often aren’t aware of the issue before they buy.”"