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서정태 忠州大學校 2002 한국교통대학교 논문집 Vol.37 No.3
Speech coding of Wideband(over 7Khz) signals is one of the currently important research topics in source coding, new applications in high quality communication systems and by standardization activities in ITU-T(International Telecommunication Union-Telecommunication Standardization Sector). This paper deals with basic concepts from traditional speech coding and their implications for wideband signals. Wideband coding by incorporating both time and frequency-domain techniques is of particular interest in order to achieve flexible solutions offering high quality at low bit rates.
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二次 長區間 豫測을 利用한 half-rate 音聲 符號化器
徐廷泰 忠州大學校 1996 한국교통대학교 논문집 Vol.31 No.2
Speech requires a large number of bits to express speech in digital form. It is essential to develop a high-performance speech coding algorithm for low bit rate which uses a limited channel capacity effectively. The researches and developments on the low bit rate speech coder have focused on the quality of synthesized sound. A dominant factor that determines the sound quality is the choice of how to model speech signal and how to estimate relevant parameters. In particular, the quality in half rate is known to depend mainly on pitch information. In this paper, a methods improving performance in low bit rate under 4.8 kbps is proposed which adopts the secondary LTP(Long Term Predictor) on the CELP(Code Excited Linear Predictor)-style speech coder, the most remarkable coding method which provides comparatively good quality in low bit rate. In the conventional CELP-style speech coder, quasi-periodic peak components are still remained after the LTP. The proposed method improves the quality of synthesized sound by eliminating the quasi periodicity effectively. It is done by performing the secondary LTP using the adaptive codebook made by excitation signals of the previous frames is proposed. Computer simulation was set to have the transmission rate of 4.8 kbps, and the performance was compared with that of the conventional band-splitted method and that of the DoD-CELP, known to be the standard speech coding method. The proposed method showed better performance in both subjective and objective measure.
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徐廷泰 충주대 산업과학기술연구소 1999 産業科學論文集 Vol.7 No.1
This paper represents a speech quality comparator for mobile system. Speech quality is an important means of estimating performance of mobile communication services in which most of the transmitted voice signals are corrupted by background noise as well as channel impairments since accurate quality assessment is directly related to end-user satisfaction and ensures to continue high performance of mobile systems. Quality information under varying noise environments has traditionally been determined using subjective tests based on human listener rating schemes such as Mean Opinion Score (MOS) and objective tests such as SegSNR.
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다중 펄스와 다중 대역 이차 장구간 예측을 이용한 CELP 음성 부호화기
서정태,최용수,강홍구,윤대희 한국음향학회 1998 韓國音響學會誌 Vol.17 No.1
본 논문에서는 낮은 비트율 CELP 음성 부호화기의 장구간 예측기의 성능 향상 방 법을 제안한다. 비트율을 낮추기 위해서는 분석 구간의 길이가 길어져야하며 이에 따라 장 구간 예측기의 성능이 저하되어 장구간 예측 후에도 준 주기성 성분이 상당량 존재하므로 백색 잡음으로 구성된 통계 코드북만으로는 이를 모델링하기 어려워진다. 제안 방법에서는 다중 대역 필터와 다중 펄스열을 이용하여 한 번 더 필터링(이차 장구간 예측)함으로써 장 구간 예측 후의 신호가 통계 코드북에 적합한 백색 잡음 형태로 되도록 모델링한다. 제안된 방법의 성능을 평가하기 위해 4.8kbps 비트율로 양자화한 후, 기존에 제안된 같은 전송률의 MBCELP와 DoD-CELP와 비교하였다. 실험 결과 제안된 방법이 기존 부호화기들에 비해 주/객관적인 음질에서 우수한 성능을 보여준다.
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徐廷泰 충주대학교 산업대학원 1999 大學院論文輯 Vol.1 No.-
VSELP is standard technique of Low Bit Rate Speech Coding.Techniques for improving the performance of VSELP-type speech coders while maintaining reasonable computational complexity are explored and,Enhanced coding algorithm is needed for efficient realization. In this paper, Regular Pulse VSELP speech coding algorithm is proposed.For evaluation of proposed coding method,4.8 kbps Regular Pulse VSELP Encoder is implemented using C language. The simulation result at 4.8 kbps bit-rate,proposed method improve speech quality.
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서정태 忠州大學校 2008 한국교통대학교 논문집 Vol.43 No.-
Monitoring of speech quality assessment in emerging heterogeneous networks is of great interest to network operators. The most efficient way to satisfy such a need is through Non-intrusive speech quality assessment. In this paper, we review a low-complexity method for monitoring the speech quality assessment. This paper reviews the development of perceptually excited models for quality assessment of speech transmission and storage systems. The main object is to predict subject mean opinion score(MOS) for non-linear, time invariant distortions such as lossy coders, channel errors or noise reduction, particularly for telecommunication application.
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서정태 한국교통대학교 2016 한국교통대학교 논문집 Vol.51 No.-
A code-book is a document used for implementing a code. A code-book contains a lookup table for coding and decoding. Low bit rate speech codec is a speech coding method used in mobile environments. It is an analysis-by-synthesis coding technique and belongs to the class of speech coding algorithms known as CELP (Code Excited Linear Prediction). Variations of this codec have been used in several standards, including GSM (Half Rate speech). A major drawback of this speech codec is its system complexity. In this paper, It is studied code-book structure analysis and code-book optimization method
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서정태 충주대 산업과학기술연구소 1996 産業科學論文集 Vol.4 No.-
In this paper, a methods improving prformance in low bit rate under 4.8kbps is proposed which adopts the secondary LTP(Long Term Predictor) on the CELP(Code Excited Linear Predictor style speech coder. Conventional CELP speech coder, quasi periodic components are still remained after LTP. The proposed methods improves the quality of Synthesized sound by eliminating the quasi periodicty effectively. It is done by dividing the residual signnal to a number of bands and subsequently eliminating once more with multi-pulse modelled to correspond with characteristics of residual signal.
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서정태 忠州大學校 2012 한국교통대학교 논문집 Vol.47 No.-
The developments on the low bit rate speech coder have focused on the quality of synthesized sound. The quality in low bit rate is known to depend mainly on pitch information. In this paper, a methods improving performance in low bit rate under 4.8 kbps is proposed which adopts the secondary LTP(Long Term Predictor) on speech coder. In addition, method which differ in the way to construct the prediction signal for LTP are proposed. It divides the excitation signal into frequency bands and constructs it with multi-pulse.
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