Speech quality enhancement and pitch-dependent bit reduction scheme for WI coders

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In this thesis, an improved SEW/REW decomposition method with pitchdependent phase generation and a noble variable bit rate (VBR) scheme are proposed to enhance the speech quality of the waveform interpolation (WI) coder and reduce the bit rate of the WI coder. In the original WI scheme, a characteristic waveform (CW) is decomposed into a slowly evolving waveform (SEW) and a rapidly evolving waveform (REW) in Cartesian coordinates. This may deteriorate the spectral shape of the reconstructed CWs. Especially, speech quality degradation is inevitable when the REW contains SEW components. To solve this problem, the proposed decomposition is performed in the magnitude domain to reduce spectral distortions. The phase of the characteristic waveforms is generated after classifying the signal into silence, unvoiced and voiced speech using the pitch value. The proposed VBR scheme is achieved by substituting white Gaussian noises with the excitation signal of silence and unvoiced speech and allocating bit rates variably. The performance of our proposed method was evaluated by the perceptual evaluation of speech quality (PESQ) score. The proposed CW modification results in the PESQ score improvement by 0.32 from the baseline speech quality, i.e., the PESQ score of 3.368. In addition, we confirmed that the required bit rate is decreased by 6.7% using the proposed novel VBR scheme. Experimental results show that our proposed algorithm achieves the improved speech quality while reducing the required bit rate compared to the conventional methods.
Advisors
Hahn, Min-Sooresearcher한민수researcher
Description
한국정보통신대학교 : 공학부,
Publisher
한국정보통신대학교
Issue Date
2009
Identifier
393111/225023 / 020064606
Language
eng
Description

학위논문(석사) - 한국정보통신대학교 : 공학부, 2009.2, [ vii, 45 p. ]

Keywords

음원 파형 보간; 음원 이용 가변 비트율; 특징 파형; Source-Controlled Variable Bit Rate; Characteristic Waveform; Waveform Interpolation

URI
http://hdl.handle.net/10203/55094
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=393111&flag=dissertation
Appears in Collection
School of Engineering-Theses_Master(공학부 석사논문)
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