Browsing by Author "Liu, WH"

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A self-calibrated speaker tracking system using both audio and video data
(2002)
Hu, J
;
Su, TM
;
Cheng, CC
;
Liu, WH
;
Wu, TI
In this paper, a self-calibrated speaker tracking system applied on both image tracking and sound source detection is proposed. The sound source estimated by microphone system is used to supply video tracking system. On the other hand, the direction of speaker detected by image tracking system is fed back to calibrate the phase distortion between microphones. Some experiments using actual devices are also done to test the performance of the proposed method. It is shown that significant improvement in source localization accuracy is possible when the camera and the microphone system are well calibrated.
Processing of speech signals using a microphone array for intelligent robots
(2005-03-01)
Hu, I
;
Cheng, CC
;
Liu, WH
;
電控工程研究所
;
Institute of Electrical and Control Engineering
For intelligent robots to interact with people, an efficient human-robot communication interface is very important (e.g. voice command). However, recognizing voice command or speech represents only part of speech communication. The physics of speech signals includes other information, such as speaker direction. Secondly, a basic element of processing the speech signal is recognition at the acoustic level. However, the performance of recognition depends greatly on the reception. In a noisy environment, the success rate can be very poor. As a result, prior to speech recognition, it is important to process the speech signals to extract the needed content while rejecting others (such as background noise). This paper presents a speech purification system for robots to improve the signal-to-noise ratio of reception and an algorithm with a multidirection calibration beamformer.
Robust beamforming of microphone array using H infinity adaptive filtering technique
(2006-03-01)
Hu, JS
;
Liu, WH
;
Cheng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In ASR (Automatic Speech Recognition) applications, one of the most important issues in the real-time beamforming of microphone arrays is the inability to capture the whole acoustic dynamics via a finite-length of data and a finite number of array elements. For example, the reflected source signal impinging from the side-lobe direction presents a coherent interference, and the non-minimal phase channel dynamics may require an infinite amount of data in order to achieve perfect equalization (or inversion). All these factors appear as uncertainties or un-modeled dynamics in the receiving signals. Traditional adaptive algorithms such as NLMS that do not consider these errors will result in performance deterioration. In this paper, a time domain beamformer using H-infinity filtering approach is proposed to adjust the beamforming parameters. Furthermore, this work also proposes a frequency domain approach called SPFDBB (Soft Penalty Frequency Domain Block Beamformer) using H-infinity filtering approach that can reduce computational efforts and provide a purified data to the ASR application. Experimental results show that the adaptive H-infinity filtering method is robust to the modeling errors and suppresses much more noise interference than that in the NLMS based method. Consequently, the correct rate of ASR is also enhanced.
Syntheses and photophysical properties of type-II CdSe/ZnTe/ZnS (core/shell/shell) quantum dots
(2005)
Cheng, CT
;
Chen, CY
;
Lai, CW
;
Liu, WH
;
Pu, SC
Syntheses of CdSe/ ZnTe/ ZnS (core/shell/shell) type-II quantum dots (QDs) are reported. Structural characterization was made via TEM, EDX, XPS and XRD. Photophysical properties were investigated via the interband emission (CdSe -> ZnTe) and its associated quantum efficiency as well as relaxation dynamics. In comparison to the weak emission (Phi(f) similar to 4 x 10(-3) in toluene) of CdSe/ ZnTe (3.9/ 0.5 nm), capping ZnS (0.4 nm in thickness) enhances the CdSe -> ZnTe interband emission by similar to 30 fold (Phi(f) similar to 0.12), whereas the peak wavelength shifts only slightly to the red. By encapsulating dihydrolipoic acid ( DHLA), water-soluble CdSe/ ZnTe/ ZnS QDs were also prepared, and they exhibited an interband emission at y930 nm with an emission yield of similar to 0.1. Femtosecond pulse excitation (lambda(ex) similar to 1200 nm) measurement estimated a two- photon absorption cross section, sigma, of similar to 70 x 10(-50) cm(4) s photon(-1) for DHLA-capped CdSe/ ZnTe/ ZnS in water, supporting its suitability for the use as near-infrared (NIR) dyes in biomedical imaging.