Weiping Tu

Enhanced Principal Component Using Polar Coordinate PCA for Stereo Audio Coding

High efficiency audio compression is the basic technology in audio involved multimedia application. Down mixing and parametric coding are efficient coding scheme with widely applications in some up to date audio codecs such as PS in EAAC+ and MPEG-Surround, and PCA stereo coding followed this idea to map two channels to one channel with maximum energy and parameterize the secondary channel. This paper investigates the conventional PCA method performance under general stereo model with multiple sound sources and different directions, and then proposes a Polar Coordinate based PCA (PC-PCA) stereo coding method. It has been proved that when multiple sound sources exist with different directions, proposed method is better than the conventional PCA method in certain conditions. A stereo codec based on PC-PCA has also been proposed to validate the performance improvement of proposed method.

A down-mixing method for 22.2 multichannel system reproduction

This paper proposes a general multichannel system reproduction method. Firstly, relative to original multichannel system, a general global model is build up by guaranteeing sound pressure and the direction of particle velocity at the receiving point constant, and making the square error of particle velocity magnitude at the receiving point as little as possible. Then the model is equivalent to a least squares problems with non-negative constraints, it can be worked out by existing mature algorithms, and the global optimal solution of simplifying multichannel system are obtained. The proposed method can be used to simplify 22.2 multichannel system to 10.2 and 8.2 multichannel system, objective and subjective experimental results demonstrate that it performs better than traditional method.

A 3D audio coding technique based on extracting the distance parameter

This paper presents a compression technique to improve the quality of three-dimensional (3D) audio produced by multiple loudspeaker channels or by headphone. The approach is based on extracting the side information of spatial sound sources within the three-dimensional space when capturing the sound sources. Different from other compression technique, the distances of sound sources are included in the side information. The separated signals of different sound sources are downmixed into one mono or stereo audio signal with the side information. The resulting downmixed signal is then compressed with traditional audio coder, resulting in a better perceptual quality of 3D audio by adding the distance parameter in the side information, and maintaining a low bit rates comparable with directional audio coding (DirAC).

Expanded three-channel mid/side coding for three-dimensional multichannel audio systems

Three-dimensional (3D) audio technologies are booming with the success of 3D video technology. The surge in audio channels makes its huge data unacceptable for transmitting bandwidth and storage media, and the signal compression algorithm for 3D audio systems becomes an important task. This paper investigates the conventional mid/side (M/S) coding method and discusses the signal correlation property of three-dimensional multichannel systems. Then based on the channel triple, a three-channel dependent M/S coding (3D-M/S) method is proposed to reduce interchannel redundancy and corresponding transform matrices are presented. Furthermore, a framework is proposed to enable 3D-M/S compress any number of audio channels. Finally, the masking threshold of the perceptual audio core codec is modified, which guarantees the final coding noise to meet the perceptual threshold constraint of the original channel signals. Objective and subjective tests with panning signals indicate an increase in coding efficiency compared to Independent channel coding and a moderate complexity increase compared to a PCA method.

Azimuthal Perceptual Resolution Model Based Adaptive 3D Spatial Parameter Coding

The spatial perceptual feature of human ears plays an important role on the quantization of spatial parameter. Human ears have the most sensitive feature for sound in frontal direction, less for the rear area, and least for the lateral sides. Traditional quantization method of spatial parameter for frontal channel pair in stereo spatial audio coding is not suitable for that of channel pairs in different directions such as lateral or rear directions in multichannel audio coding. An azimuthal perceptual resolution model based adaptive spatial parameter coding for 3D audio multichannel signals is proposed in this paper. Based on the omnibearing and non-uniform azimuthal perceptual resolution model of human ears for sound sources in different directions, quantization values of spatial parameters can be estimated adaptively according to the location and configuration of channel pairs in arbitrary directions. The density features of quantization steps for spatial parameters of channel pairs in arbitrary directions are corresponding to the non-uniform azimuthal perceptual resolution of human ears. So that the quantization noise can be effectively reduced under the directional perceptual threshold with the improved reproduced spatial sound quality.

Three-dimensional panning by four loudspeakers and its solution

This paper proposes a 3D panning method based on particle velocity and sound pressure by four loudspeakers for synthesizing a virtual sound source. Firstly, according to the requirements of maintaining sound physical properties strictly, the distribution coefficients of four loudspeakers are calculated by the coordinates of four loudspeakers and a virtual sound source. If the distribution coefficients is not all positive, we maintain the direction of particle velocity and sound pressure to get a series of feasible solutions. Then optimal distribution coefficients of four loudspeakers are chosen through minimizing the error of particle velocity from these feasible solutions. Objective experiment demonstrates that this method can make mean error of sound pressure at most about 19.3% lower than Andos method around spherical center in equatorial plane. Subjective experiment shows that the proposed method performs better than Andos method.

Reduction of Multichannel Sound System Based on Spherical Harmonics

In order to meet peoples demand for 3D audio in family, its a critical problem to recreate a 3D spatial sound field with few loudspeakers. In this paper, we introduce a L- to L-1-channel reduction method based on spherical harmonic decomposition and sound field of head can be perfectly reproduced. When loudspeakers are too few to perfectly reproduce the sound field of head, we ensure low distortions of sound field at ears. On this basis, multichannel reduction algorithm from L- to M-channel system is proposed. As an example, reduction of NHK 22.2 system has been implemented and eleven loudspeaker arrangements from 22 to 6 channels are derived. Results show the sound field of head can be reproduced perfectly until 10 channels and 8-, 6-channel systems can keep low distortions at ears. Compared with Andos multichannel conversion method by subjective evaluation, our proposed method is better in terms of sound localization.

The Analysis for Binaural Signal’s Characteristics of a Real Source and Corresponding Virtual Sound Image

3D Audio System could rebuild more realistic and immersive sound effects. The existing 3D audio reconstruction methods mainly consider the physical characteristics of sound filed, less take head’s effect on sound transmission process into account. However, when human is located in the sound field, there will have an obvious deviation between perceptual sound image and reconstructed image. Some researchers considered head’s effects on the reconstruction of sound field, but they only use simple head model to reproduce sound field in some certain loudspeaker configurations. Therefore, if we want to reconstruct an ideal sound filed, we need to analyze head’s effects on the reconstruction of sound field in detail. Thus in this paper, we analyzed and compared binaural signal’s characteristics under different loudspeaker configurations and gains. The analysis results may be act as a primary reference for further research about sound field reconstruction etc.

3D Panning Based Sound Field Enhancement Method for Ambisonics

When conventional first order Ambisonics system uses four loudspeaker with platonic solid layout to reconstruct sound field, the 3D acoustic field effect is limited. A new signal distribution method is proposed to enhance the reproduced field without increasing loudspeakers. First, a platonic solid is extended to get more new vertexes, based on the traditional Ambisonics signal distribution method, original field signal is distributed to loudspeakers at original and new vertexes of platonic solid. Second, signals of loudspeakers at new vertexes are distributed to loudspeakers at original vertexes by a new 3D panning method, then loudspeakers at new vertexes of platonic solid are deleted, only original vertexes of platonic solid are left. The proposed method can improve the quality of the reconstructed sound field and will not increase the complexity of loudspeaker layout in practice. Results are verified through objective and subjective experiments.

Automatic Multichannel Simplification with Low Impacts on Sound Pressure at Ears

People hope to use minimum arrangement of loudspeakers to reproduce the experience of the film 3D sound at home. Although the Andos conversion can convert n- to m-channel sound system by maintaining the sound pressure at the origin, it is time-consuming and expensive to use lots of subjective evaluations to distinguish the experience of spatial sound reproduced by m-loudspeaker arrangements. To solve this problem, we not only ensure the sound pressure at the origin invariably, but also limit the absolute error of sound pressure at ears to a given threshold or less while simplifying from n- to n-1-channel, and an automatic simplification algorithm from n- to m-channel sound system is proposed. The 22.2 multichannel sound system without two low-frequency effect channels as an example can be simplified to eight channels automatically and the total loudspeaker arrangements is 23. The subjective evaluation is comparable to that of the Andos conversion and the cost of subjective evaluation is saved.