Outdoor/Indoor Transmission Class (OITC) rating is a way to estimate a wall or door’s ability to reduce typical transportation noise. It is determined in accordance with ASTM E 1332, a standard classification for rating outdoor-indoor sound reduction. Unlike the STC, which is based on a noise spectrum targeting speech sounds, OITC uses a source noise spectrum that considers frequencies down to 80 Hz (aircraft/rail/truck traffic) and is weighted more to lower frequencies. The OITC value is typically used to rate, evaluate, and select exterior glazing assemblies.