음성 부호화기 전송률 구조 연구

서정태 한국교통대학교 2018 한국교통대학교 논문집 Vol.53 No.-

Linear predictive coding (LPC) is a tool used mostly in audio signal processing and speech processing for representing the spectral envelope of a digital signal of speech in compressed form, using the information of a linear predictive model. It is one of the most powerful speech analysis techniques, and one of the most useful methods for encoding good quality speech at a low bit rate. This speech coder was standardized by ITU-T. The coder operates on each 30ms frame of 16-bit speech signals sampled at 8 Khz and generates a compressed bit-stream having variable rates respectively. It has a look-ahead delay of 7.5 ms and uses algebraic code excited linear prediction algorithm for the low bit-rate and Multi-Pulse Maximum Likelihood Quantization (MP-MLQ) algorithm for the high bit-rate modes. The decoder supports an inherent packet loss concealment algorithm.

정규 펄스를 이용한 VSELP 음성 부호화기

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.

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.

음질평가 방법의 비교평가

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.

음질 평가 기술 연구

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.

음성 부호화기의 코드북 구성 연구

서정태 한국교통대학교 2015 한국교통대학교 논문집 Vol.50 No.-

Speech coding is an application of data compression of digital signals containing speech. It uses speech parameter prediction to model the speech signal. A fast code-book search method for code excited linear predictive coding of speech is described. The method relies on using a vector-sum code-book where the cross correlation of any pair of basis vectors is odd-symmetric. The cost function for code-book search is a constant with respect to the search, and a simple sign detection procedure is used to locate the optimum codeword with a complexity almost independent of the code-book size. In this paper, a methods improving performance in low bit rate is studied with a structure of code-book on the Code Excited Linear Predictor style speech coder. It is the most remarkable coding method which provides comparatively good quality in low bit rate.

음성 부호화기 다중 펄스 연구

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.

낮은 비트 율 음성부호화기의 코드 북 최적화 연구

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

서브밴드를 이용한 넓은 대역 음성 부호화기

徐廷泰 충주대 2004 産業科學論文集 Vol.12 No.-

This paper describes a Sub Band coding scheme for wideband speech signal. In this analyzed coder, band splitting approach is used. The lower band speech is encoded with ITU-T G.729E, which is known as a high-quality narrow band speech coder at 8/11.8 kbps. Since the encoding of the lower band is independent of upper band signal, the output speech of the decoder can be selected to be narrowband or wideband according to the channel conditions. Possible wideband applications include high-quality audio conferencing, digital AM broadcasting and third-generation wireless communications

분석/합성 음성 부호화기(VSELP)

徐廷泰 忠州大學校 1998 한국교통대학교 논문집 Vol.33 No.2

In recent years, A good technique of low bit rate speech coder is ABS(Analysis by Synthesis) style coder. This paper describes VSELP(Vector sum Error Linear prediction) speech coder. To demonstrate the performance of the VSELP coder, VSELP coder is quantized with 4.8 kbps and it is compared with conventional CELP(Code Excited Linear Prediction) style coder.