In 2004 the ISO/MPEG Audio standardization group started a new work item on efficient and backward-compatible coding of high-quality multichannel sound using parametric coding techniques. Finalized in the fall of 2006, the resulting MPEG Surround specification allows the transmission of surround sound at bit rates that have been commonly used for coding of mono or stereo sound. The results of the standardization process are summarized by describing the underlying ideas and providing an overview of the MPEG Surround technology. The performance of the scheme is characterized by the results of recent verification tests. These tests include several operation modes as they would be used in typical application scenarios to introduce multichannel audio into existing audio services.

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MPEG Surround – the ISO/MPEG Standard for Efficient and Compatible Multi-Channel Audio Coding

An overview of the recently finalized ISO/MPEG standard for multichannel audio compression MPEG Surround is provided. This audio compression scheme enables backwardcompatible multichannel audio coding and transmission at unsurpassed coding efficiency. This is achieved by generating a mono, stereo, or matrixed-surround compatible down mix, which can be transmitted using any existing mono or stereo service, extended with a small amount of parametric side information that describes the perceptually relevant spatial properties of the original multichannel content. The concepts behind spatial parameterization are outlined, and the architecture of the MPEG Surround system is explained. Results of subjective evaluations are included to demonstrate its efficiency.

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Background, concept, and architecture for the recent MPEG surround standard on multichannel audio compression

The invention relates to the technical field of audio encoding and/or decoding technologies, and thus concerns an overall encoding procedure and associated decoding procedure. The encoding procedure involves at least two signal encoding processes (S1-S3) operating on signal representations of a set of audio input channels, as well as residual encoding (S7-S8). It also involves a dedicated process (S4-S6) to estimate and encode energies of the audio input channels. Each encoding process is associated with a corresponding decoding process. In the overall decoding procedure the decoded signals from each encoding process are preferably combined such that the output channels are close to the input channels in terms of energy and/or quality. Normally, the combination step also adapts to the possible loss of one or more signal representation in part or in whole, such that the energy and quality is optimized with the signals at hand in the decoder. In this way, the overall quality of the output channels is improved.

Energy conservative multi-channel audio coding

This paper describes novel methods for evoking a multichannel audio experience over stereo headphones. In contrast to the conventional convolution-based approach where, for example, five input channels are filtered using ten head-related transfer functions, the current approach is based on a parametric representation of the multichannel signal, along with either a parametric representation of the head-related transfer functions or a reduced set of head-related transfer functions. An audio scene with multiple virtual sound sources is represented by a mono or a stereo downmix signal of all sound source signals, accompanied by certain statistical (spatial) properties. These statistical properties of the sound sources are either combined with statistical properties of head-related transfer functions to estimate "binaural parameters" that represent the perceptually relevant aspects of the auditory scene or used to create a limited set of combined head-related transfer functions that can be applied directly on the downmix signal. Subsequently, a binaural rendering stage reinstates the statistical properties of the sound sources by applying the estimated binaural parameters or the reduced set of combined head-related transfer functions directly on the downmix. If combined with parametric multichannel audio coders such as MPEG Surround, the proposed methods are advantageous over conventional methods in terms of perceived quality and computational complexity.

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Binaural rendering in MPEG surround

Spatial hearing enables translation of an auditory scene into a perceived 3-D image by interpreting the acoustic cues related to the sounding objects, their locations, and the physical characteristics of the space Spatial audio production requires multichannel audio signals in order to convey this information and increase the realism of a real or virtual environment for applications such as the home entertainment, virtual reality, and remote collaboration As demand to spatial audio continues to expand, efficient coding of multichannel audio content becomes more and more important This paper provides an overview of some well-known multichannel audio coding techniques and presents a new coding framework for improving the objective fidelity of the decoded signals A closed-loop encoding system based on analysis-by-synthesis (AbS) principle applied on the MPEG surround (MPS) architecture is described Comparison results are presented, which show that significant improvements can be achieved with a closed-loop system instead of the conventional open-loop system

Multichannel Audio Coding Based on Analysis by Synthesis

We propose in this paper a backward-compatible multichannel audio codec. This codec represents a multichannel audio input signal by a down mix and parametric data. In order to enable backward compatibility, it is necessary to have the possibility of exerting control over the down-mixing procedure. At the same time, in order to achieve a high coding efficiency, both signal and perceptual redundancies should be exploited. In this paper, we describe a codec that unifies the above-mentioned conditions: backward compatibility and exploitation of both signal and perceptual redundancies. The codec combines a high audio quality and a low parameter bit rate. Moreover, its design is flexible, examples of which are the scalability of the audio quality to (in principle) transparency and the possibility to preserve the correlation structure of the original input signals by using synthetic signals. A stereo backward compatible version of the proposed codec is used as a component of the recently standardized MPEG Surround multichannel audio codec.

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L.F. Villemoes

Papers

A Backward-Compatible Multichannel Audio Codec