The term Dolby Surround covers the evolution of multichannel sound technologies developed by Dolby Laboratories for cinema and home use. The technology began in the analog era with phase-matrix systems known as 4:2:4, where four audio channels were encoded within two stereo channels and subsequently recovered by an intelligent decoder, with Dolby Pro Logic being the most famous example due to its active signal steering. Later, the technology migrated to the digital domain with discrete and independent channel formats, evolving from the classic compressed Dolby Digital to high-resolution formats like Dolby Digital Plus and Dolby TrueHD, which offers lossless audio identical to the studio master.