What's the difference between Dolby Digital 5.1 and Dolby Digital Plus?

Dolby Digital (AC-3) is the legacy codec that supports up to 5.1 channels, while Dolby Digital Plus (E-AC-3) uses lossy compression to handle 5.1, 7.1, and can transport Dolby Atmos metadata for object-based sound. DD+ was designed for streaming and can be down-mixed to standard Dolby Digital for older decoders, so enabling DD+ is preferable when all devices support it.