Dolby AC-4 and Dolby Atmos are not the same as the two terms are describing different aspects of audio delivery. Dolby AC-4 describes the underlying audio technology including the audio compression technology, metadata support and system aspects. Dolby Atmos describes Dolby's immersive audio experience that can be delivered by multiple Dolby audio technologies including Dolby AC-4 and Dolby Digital Plus. Dolby Atmos can be viewed as the next logical step beyond traditional surround sound. Dolby AC-4 is the natural successor to Dolby Digital Plus and Dolby Digital.