Insulation performance of partitions (walls and floor-ceiling assemblies) is rated in terms of Sound Transmission Class (STC) and Impact Insulation Class (IIC).  Higher ratings mean better noise insulation.
Airborne noise insulation ratings must be at least STC 50 in lab tests or STC 45 in field tests.  Impact noise insulation ratings for floor-ceiling assemblies also must be at least IIC 50 in lab tests or IIC 45 in field tests. Interior noise levels due to exterior sources must not exceed 45 dB in any habitable room.
The current version of the code (2020) lists these STC and IIC requirements, along with specific ASTM test method references.  This issue also changed the section number from 1207, used in prior versions.
It now states that, alternatively, the sound transmission of walls and floor-ceiling assemblies may be established by engineering analysis based on a comparison of walls, partitions and floor-ceiling assemblies having sound ratings as determined by ASTM test procedures.
The previous version of the code (2016) lists only the STC and IIC requirements from earlier issues, but also introduces the term "sleeping units" as well as dwellings so as to include live-work spaces.
An earlier version of the code (2007) included the same numerical limits for noise insulation rating between dwellings, along with extensive technical standards, references and details of the methods used for compliance assessment.