Sound Transmission Class (STC) is a laboratory rating commonly used to evaluate a building partition’s ability to stand out from the airborne sound transfer. ASTC ratings match up with the same assembly tested under field conditions. A field test can determine the rating of a partition for consent with building codes by placing a sound source on one side of the demising wall/ceiling/floor under test, and measuring the sound levels in the source room and receiver rooms on both sides of the assembly. Measurements are also taken to determine the ambient sound and resonance in the receiver room, along with the room geometry. The combination of all this data is used to determine the ASTC rating.  STC rating of 38-42 is considered good soundproofing for residential. STC rating of 50-65 is professional, commercial soundproofing for recording studios, etc. These terms and definitions are related to Sound Transmission Class and will help provide the full picture of how sound is measured.