Browsing by Author "Lee, Chih-Chung"

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Automotive virtual surround audio system
(2009-07-16)
Bai, Ming-Sian
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Lee, Chih-Chung
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Chen, Hui-Wen
An automotive virtual surround audio system is implemented in an automobile to receive left- and right-channel audio sources. A synthesizer receives the left- and right-channel audio sources to extend the sources into temporary rear-left and rear-right audio sources. A weighting device receives the left- and right-channel audio sources to perform a weighting operation and produce temporary front-left and front-right audio sources. A first filter receives the temporary front-left and front-right audio sources to perform a filtering operation and produce virtual front-left and front-right audio sources. A second filter receives the temporary rear-left and rear-right audio sources to perform a filtering operation and produce virtual rear-left and rear-right audio sources. Thus, the virtual audio image position is reproduced.
Comparative study of audio spatializers for dual-loudspeaker mobile phones
(2007-01-01)
Bai, Mingsian R.
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Shih, Geng-Yu
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Lee, Chih-Chung
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機械工程學系
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Department of Mechanical Engineering
MPEG-1, layer 3 handsets equipped with dual loudspeakers and three-dimensional audio modules have received much attention in the market of consumer electronics. To create spatial impression during audio reproduction, the head-related transfer function (HRTF) and the crosstalk cancellation system (CCS) are key elements in many audio spatializers. However, there are many factors that one should take into account during the design and implementation stages of an audio spatializer in the handset application. In the paper, a comprehensive study was undertaken to compare various audio spatializers for use with dual- loudspeaker handsets, in the context of inverse filtering strategies. Two deconvolution approaches, the frequency-domain method and the time-domain method, are employed to design the required inverse filters. Different approaches to design audio spatializers with the HRTF, CCS, and their combination are compared. In particular, two modified CCS approaches are suggested. Issues in the implementation phase such as regularization, complex smoothing, and structures of inverse filters are also addressed in the paper. Comprehensive objective and subjective tests were conducted to investigate the aforementioned aspects of audio spatializers. The data obtained from the subjective tests are processed by using the multianalysis of variance to justify statistical significance of the results. (c) 2007 Acoustical Society of America.
Comparative Study of Design and Implementation Strategies of Automotive Virtual Surround Audio Systems
(2010-03-01)
Bai, Mingsian R.
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Lee, Chih-Chung
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機械工程學系
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Department of Mechanical Engineering
A comprehensive study was conducted to compare various design and implementation strategies of automotive virtual surround audio. Nowadays there is increased proliferation of multichannel audiovisual systems used in cars. However, the interior of a car is known as a notorious listening environment due to reflections in a confined space. nonideal user/loudspeaker positions, and ambient noise. It is then desirable to develop audio systems that are capable of rendering quality spatial sound fields in harsh car environments. Four design approaches are proposed for two-channel and 5.1-channel input. For two-channel input a method of reverberation-based upmixing with inverse filtering and another method of up/down mixing with weighting and delay are presented. The upmixing algorithm is used to convert two-channel signals to four-channel signals, while the downmixing algorithm does just the opposite. Inverse filters are employed to position the virtual sound images according to the 5.1 configuration. For 5.1-channel input a method of downmixing with inverse filtering and another method of downmixing with weighting and delay are presented. These processing algorithms have been practically implemented on a car. Simulations and experiments were conducted for validating the proposed spatial audio systems. Subjective listening tests were also conducted to compare these methods with the data processed by multivariate analysis of variance (MANOVA). The experimental results reveal that inverse filtering is most effective for single-passenger mode. especially at rear seats. However, if there is more than one passenger, the alternative methods may be more appropriate in terms of rendering performance and computational complexity.
Loudspeaker system having sensorless bass compensation
(2007-09-20)
Bai, Ming-Shian
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Lee, Chih-Chung
;
Lin, Chien-Liang
The present invention compensates bass frequency for a loudspeaker without using any sensor. The strength and stability of the loudspeaker are enhanced and the working frequency is lowered too. Adaptive loudnesses for various spaces are set. And the parameter drift owing to long-term operation is restrained as well.
Objective and subjective analysis of effects of listening angle on crosstalk cancellation in spatial sound reproduction
(2006-10-01)
Bai, Mingsian R.
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Lee, Chih-Chung
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機械工程學系
;
Department of Mechanical Engineering
A comprehensive study was conducted to explore. the effects of listening angle on crosstalk cancellation in spatial sound reproduction using two-channel stereo systems. The intention is to establish a sustainable configuration of crosstalk cancellation system (CCS) that best reconciles the separation performance and the robustness against lateral head movement, not only in theory but also in practice. Although crosstalk can in principle be suppressed using multichannel inverse filters, the CCS does not lend itself very well to practical application owing to the fact that the sweet spot is being so small. Among the parameters of loudspeaker deployment, span angle is a crucial factor that has a profound impact on the separation performance and sweet spot robustness achievable by the CCS This paper seeks to pinpoint, from a more comprehensive perspective, the optimal listening angle that best reconciles the robustness and performance of the CCS. Two kinds of definitions of sweet spot are employed for assessment of robustness. In addition to the point source model, head related transfer functions (HRTF) are employed as the plant models in the simulation to emulate more practical localization scenarios such as the high-frequency head shadowing effect. Three span angles including 10, 60, and 120 deg are then compared via objective and subjective experiments. The Friedman test is applied to analyze the data of subjective experiments. The results indicate that not only the CCS performance but also the panning effect and head shadowing will dictate the overall performance and robustness. The 120-deg arrangement performs comparably well as the standard 60-deg arrangement, but is much better than the 10-deg arrangement. (c) 2006 Acoustical Society of America.
Subband approach to bandlimited crosstalk cancellation system in spatial sound reproduction
(2007)
Bai, Mingsian R.
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Lee, Chih-Chung
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機械工程學系
;
Department of Mechanical Engineering
Crosstalk cancellation system (CCS) plays a vital role in spatial sound reproduction using multichannel loudspeakers. However, this technique is still not of full- blown use in practical applications due to heavy computation loading. To reduce the computation loading, a bandlimited CCS is presented in this paper on the basis of subband filtering approach. A pseudoquadrature mirror filter (QMF) bank is employed in the implementation of CCS filters which are bandlimited to 6 kHz, where human's localization is the most sensitive. In addition, a frequency-dependent regularization scheme is adopted in designing the CCS inverse filters. To justify the proposed system, subjective listening experiments were undertaken in an anechoic room. The experiments include two parts: the source localization test and the sound quality test. Analysis of variance (ANOVA) is applied to process the data and assess statistical significance of subjective experiments. The results indicate that the bandlimited CCS performed comparably well as the fullband CCS, whereas the computation loading was reduced by approximately eighty percent.