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v3.0, 20040325, ME

Session J Sunday, May 9 15:30 h–18:30 h
Spatial Audio Coding
Chair: Erik Schuijers, Philips Digital Systems Laboratories, Eindhoven, The Netherlands

J-1 High-Quality Parametric Spatial Audio Coding at Low Bit Rates—Jeroen Breebaart1, Steven van de Par1, Armin Kohlrausch1,2, Erik Schuijers3
Philips Research Laboratories, Eindhoven, The Netherlands
Eindhoven University of Technology, Eindhoven, The Netherlands
Philips Digital Systems Labs, Eindhoven, The Netherlands
Recently, so-called binaural cue coding schemes have been introduced. These audio coding schemes transmit two perceptually relevant sound localization cues (i.e., level and time differences between the input channels), combined with a mono audio signal. Although these schemes are able to reconstruct the locations of various sound sources quite effectively, other aspects of the spatial ambience (such as the spatial diffuseness of reverberation) cannot be captured in this way. In this paper we present an extension to these spatial coding schemes, which comprises, in addition, a spatial sound-field parameter that is able to capture ambience properties. Experiments show that the combination of three spatial parameters enables highly efficient, high-quality audio representations.
J-2 Low-Complexity Parametric Stereo Coding—Erik Schuijers1, Jeroen Breebaart2, Heiko Purnhagen3, Jonas Engdegård3
Philips Digital Systems Laboratories, Eindhoven, The Netherlands
Philips Research Laboratories, Eindhoven, The Netherlands
Coding Technologies, Stockholm, Sweden
Parametric stereo coding is a technique to efficiently code a stereo audio signal as a monaural signal plus a small amount of stereo parameters. The monaural signal can be encoded using any audio coder. The stereo parameters can be embedded in the ancillary part of the mono bit-stream creating backwards mono compatibility. In the decoder, first the monaural signal is decoded after which the stereo signal is reconstructed from the stereo parameters. In this paper a low- complexity decoder solution is described based on complex-modulated filter banks. Combinations of the parametric stereo decoder with both a parametric coding scheme and with aacPlus will be elucidated.
J-3 Synthetic Ambience in Parametric Stereo CodingJonas Engdegård, Heiko Purnhagen, Jonas Rödén, Lars Liljeryd, Coding Technologies, Stockholm, Sweden
Parametric stereo coding in combination with an efficient coder for the underlying monaural audio signal results in the most efficient coding scheme for stereo signals at very low bit rates available today. While techniques for lateral localization have been studied since early intensity stereo coding tools, synthesis of stereophonic ambience was only recently applied in parametric stereo coding systems. This paper studies different techniques for synthetic ambience generation in the context of parametric stereo coding systems and discusses their mono-compatibility. Implementations of these techniques in combination with mp3PRO and aacPlus are presented together with experimental results.
J-4 Efficient Bit Distribution Strategy for Stereophonic Audio CodersSarat Chandra Vadapalli, Vinod Prakash, Ittiam Systems Pvt. Ltd., Bangalore, India
Maintenance of audio quality under the resource constraints on embedded platforms is very crucial. One of the major factors affecting the quality of stereophonic audio coders is the method of distribution of bits across channels of a stereo pair. Conventional approaches use perceptual entropy, a computationally intensive metric, to distribute bits across channels. Improper computation or absence of this metric can severely degrade the audio quality. This paper presents an efficient and robust scheme to distribute the bits across channels, without using perceptual entropy, while still maintaining the audio quality. In the proposed scheme, the bit allocation for both channels is performed simultaneously, by allocating bits from a common bit pool. A detailed example illustrating this scheme is presented.
J-5 Backward Linear Prediction for Lossless Coding of Stereo AudioJean-Luc Garcia, Philippe Gournay, Roch Lefebvre, University of Sherbrooke, Sherbrooke, Quebec, Canada
Lossless audio coding aims at achieving the lowest possible bit rate for transmission or storage of audio without any loss of information. This is usually done by first removing redundancy from the audio signal, and then applying entropy coding to the residual signal. Linear prediction (LP), when applied to monophonic signals, is a very effective way to remove redundancy. It produces minimum-phase predictors that are efficiently compressed by combining vector quantization with a meaningful representation of the LP coefficients (such as the LSFs). When applied to stereo signals, however, joint channel prediction often produces nonminimum-phase predictors, whose quantization requires a high bit rate and poses stability problems. In this paper we show that backward estimation of the LP coefficients (where those are estimated at the decoder, on the past decoded signal) solves most of the problems associated with the use of joint channel prediction in a lossless audio coder.

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