Spatial Audio Processing: MPEG Surround and Other Applications
by Jeroen Breebaart, Christof Faller
6.2 Spatial audio coding
6.2.1 Concept
The concept of spatial audio coding as employed in the MPEG Surround standard [138] is outlined in Figure 6.1. A multi-channel input signal is converted to a down-mix by an MPEG Surround encoder. Typically, the down-mix is a mono or a stereo signal, but more down-mix channels are also supported (for example a 5.1 down-mix from a 7.1 input channel configuration). The perceptually relevant spatial properties of the original input signals that are lost by the down-mix process are captured in a spatial parameter bitstream. The down-mix can subsequently be encoded with an existing compression technology. In the last encoder step, the spatial parameters are combined with the down-mix bitstream by a multiplexer to form the output bitstream. Preferably, the parameters are stored in an ancillary data portion of the down-mix bitstream to ensure backward compatibility.
The right panel of Figure 6.1 outlines the MPEG Surround decoding process. In a first stage, the transmitted bitstream is split into a down-mix bitstream and a spatial parameter stream. The down-mix bitstream is decoded using a legacy decoder. Finally, the multi-channel output is constructed by an MPEG Surround decoder based on the transmitted spatial parameters.
The use of an MPEG Surround encoder as a pre-processor for a conventional (legacy) codec (and a corresponding post-processor in the decoder) has important advantages over existing multi-channel compression methods.
- The parametric ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access