Spatial audio coding and MPEG surround

Abstract

Surround sound has been widely utilized in cinemas for decades, but wide adoption of home cinema surround was only enabled recently by the digital video disc (DVD). While a compact disc (CD) stores its stereo audio content uncompressed as 16-bit PCM at a sampling rate of 44.1 kHz, the DVD stores its six multichannel surround channels (five main audio channels plus a low-frequency effects channel) compressed with the perceptual audio coder AC-3 from Dolby Laboratories. The multichannel surround signal would require too much storage space on the DVD and thus it is compressed. The most prominent perceptual audio coder is MP3 (MPEG-1 Layer 3). Being a relatively old audio coder it only supports up to two audio channels. Many perceptual audio coders can also code multichannel surround signals and achieve roughly a compression ratio of 10. Spatial audio coding is motivated by the need to code multichannel audio at lower bitrates. It enables coding of multichannel audio at bitrates comparable with mono or two-channel stereo bitrates. Thus, spatial audio coding can enable multichannel surround for applications where the bitrate is constrained to a mono or stereo bitrate. Further, spatial audio coding can be compatible with mono or stereo, facilitating upgrading of existing mono and stereo services to multichannel surround. This chapter is organized as follows. Section 22.2 discusses multichannel surround and its benefits compared with the widely used stereo system. In Sect. 22.3, spatial audio coding is discussed and motivated in the context of conventional perceptual audio coding and matrix surround. In order to explain and motivate spatial audio coding, basic spatial hearing knowledge is presented in Sect. 22.4. The application of these principles to audio coding and spatial audio coding is explained in Sect. 22.5. Aspects of the commercially available MP3 Surround audio coder and the standards-based MPEG Surround coder are discussed in Sect. 22.6. Conclusions are presented in Sect. 22.7. © 2009 Springer Science+Business Media, LLC.