Dynamic Distortion Limiter (DDL)
WARNING: This page is about a different car, the 2008 Pontiac G8. However, it is still accessible from the selected car via links, so may be relevant.
With Dynamic Distortion Limiter (DDL), the audio system limits the amount of audio distortion that can be heard. The DDL system can only be adjusted while the radio is on. When the distortion level reaches a preset limit, the radio automatically reduces the volume until the distortion is reduced. The DDL adjustment range is between OFF and CUR 3