• Title/Summary/Keyword: CELP

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Implementation of a CELP coder based on optimum quantization of the LPC coefficients (LPC 계수의 최적 양자화에 기초한 음성 코더 구현)

  • Lee, W.J.;Park, J.T.;Chang, T.G.
    • Proceedings of the KIEE Conference
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    • 2001.07d
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    • pp.2516-2518
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    • 2001
  • The quantization of the LPC parameters is a very important aspect of the speech compression algorithm. This paper analyzes the quantization effect of the LPC coefficients and presents the implementation of a fixed-point CELP coder based on the LPC analysis.

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An Algorithm to Reduce the Pitch Computational amount using Modified Delta Searching in CELP Vocoders (CELP 보코더에서 델타 피치 검색 방법 개선에 대한 연구)

  • Ju, Sang-Gyu
    • Proceedings of the KAIS Fall Conference
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    • 2010.05a
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    • pp.269-272
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    • 2010
  • In this paper, we propose the computation reduction methods of delta pitch search that is used in G.723.1 vocoder. In order to decrease the computational amount in delta pitch search the characteristic of proposed algorithms is as the following. First, scheme to reduce the computation amount in delta pitch search uses NAMDF. Developed the second scheme is the skipping technique of lags in pitch searching by using the threshold value. By doing so, we can reduce the computational amount of pitch searching more than 64% with negligible quality degradation.

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Evaluation on the Lightning Breakdown Voltages of Palm Oil and Coconut Oil under Non-Uniform Field at Small Gap Distances

  • Thien, Yee Von;Azis, Norhafiz;Jasni, Jasronita;Kadir, Mohd Zainal Abidin Ab;Yunus, Robiah;Ishak, Mohd Taufiq;Yaakub, Zaini
    • Journal of Electrical Engineering and Technology
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    • v.11 no.1
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    • pp.184-191
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    • 2016
  • In recent years, there are a number of studies that have been carried out to explore the alternative for Mineral Oil (MO) as dielectric insulating fluid in transformers due to the increasing tight regulation on safety and environment. Vegetable oils have been identified as suitable candidate since it is biodegradable, non-toxic and high flash/fire points which ensure more in-service safety. Among the types of vegetable oils considered for transformers application are Palm Oil (PO) and Coconut Oil (CO). This paper presents an experimental study on the lightning breakdown voltages of PO and CO under non-uniform electric field based on needle-sphere electrodes configuration at 3 small gap distances. The type of PO used in this study is Refined Bleached and Deodorized Palm Oil (RBDPO) Olein. The main focus of this study is to examine the lightning breakdown performance of RBDPO and CO under different test conditions and assess its suitability as dielectric insulating fluid in transformers. The effect of voltage polarities (positive and negative) and testing methods (rising-voltage, up-and-down and multiple-voltage) were investigated. The data obtained from all tests were analysed by Weibull distribution in order to determine the withstand voltages for each type of oils. It was found that the breakdown voltages of RBDPO and CO are comparable with MO under positive lightning impulse. Under negative lightning impulse, the breakdown voltage of MO is slightly higher than RBDPO and CO. There is no significant effect of testing methods and voltage polarities on lightning breakdown voltages of RBDPO and CO. Based on the statistical analysis, it is found that the breakdown voltages of RBDPO and CO at 1% probability are slightly lower than MO.

Real-time implementation of the 2.4kbps EHSX Speech Coder Using a $TMS320C6701^TM$ DSPCore ($TMS320C6701^TM$을 이용한 2.4kbps EHSX 음성 부호화기의 실시간 구현)

  • 양용호;이인성;권오주
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.29 no.7C
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    • pp.962-970
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    • 2004
  • This paper presents an efficient implementation of the 2.4 kbps EHSX(Enhanced Harmonic Stochastic Excitation) speech coder on a TMS320C6701$^{TM}$ floating-point digital signal processor. The EHSX speech codec is based on a harmonic and CELP(Code Excited Linear Prediction) modeling of the excitation signal respectively according to the frame characteristic such as a voiced speech and an unvoiced speech. In this paper, we represent the optimization methods to reduce the complexity for real-time implementation. The complexity in the filtering of a CELP algorithm that is the main part for the EHSX algorithm complexity can be reduced by converting program using floating-point variable to program using fixed-point variable. We also present the efficient optimization methods including the code allocation considering a DSP architecture and the low complexity algorithm of harmonic/pitch search in encoder part. Finally, we obtained the subjective quality of MOS 3.28 from speech quality test using the PESQ(perceptual evaluation of speech quality), ITU-T Recommendation P.862 and could get a goal of realtime operation of the EHSX codec.c.

A Fast Pitch Searching Algorithm Using Correlation Characteristics in CELP Vocoder (상관관계 특성을 용한 CELP 보코더의 고속 피치검색 알고리듬)

  • Lee, Joo-Hun;Bae, Myung-Jin;Ann, Sou-Guil
    • The Journal of the Acoustical Society of Korea
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    • v.13 no.2E
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    • pp.20-25
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    • 1994
  • The major drawback to the Code Excited Linear Prediction(CELP) type vocoders is their large computational requirements. In this paper, a simple method is proposed to reduce the pitch searching time in the pitch filter almost without degradation of quality. Bease upon the observational regularity of the correlation function of speech, the searching range can be restricted to the positive side in pitch search. This is done by skipping the negative side with the width which is estimated from the previous positive envelope. In addition to that, the maximum number of available lags can be limited by the threshold, $L_T$, which is set on 58 empirically. So, only the limited numbers of lags are considered in pitch search, which is less than a half of that of the full search method. By using the proposed method in pitch search, its required computations are greatly reduced. Experimental result shows 51% time reduction almost without lowering the speech quality in segmental SNR measure.

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A Simple and Fast Pitch Search Algorithm Using a Modified Skipping Technique in CELP Vocoder (개선된 Skipping 기법을 이용한 CELP 보코더에서의 고속피치검색 알고리듬)

  • Lee, Joo-Hun;Bae, Myung-Jin;Kwon, Choon-Woo
    • The Journal of the Acoustical Society of Korea
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    • v.14 no.2E
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    • pp.33-36
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    • 1995
  • Based on the Characteristics of the correlation function of speech signal, the skipping technique can reduced the computation time considerably with a little degradation of speech quality. To improve the speech quality of the skipping technique, we use the reduced form of the correlation function to check the sign of the correlation value before the match score is calculated. The experimental results show that this modified skipping technique can reduce the computation time in pitch search over 35% compared with the traditional full search method without quality degradation.

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A MFCC-based CELP Speech Coder for Server-based Speech Recognition in Network Environments (네트워크 환경에서 서버용 음성 인식을 위한 MFCC 기반 음성 부호화기 설계)

  • Lee, Gil-Ho;Yoon, Jae-Sam;Oh, Yoo-Rhee;Kim, Hong-Kook
    • MALSORI
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    • no.54
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    • pp.27-43
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    • 2005
  • Existing standard speech coders can provide speech communication of high quality while they degrade the performance of speech recognition systems that use the reconstructed speech by the coders. The main cause of the degradation is that the spectral envelope parameters in speech coding are optimized to speech quality rather than to the performance of speech recognition. For example, mel-frequency cepstral coefficient (MFCC) is generally known to provide better speech recognition performance than linear prediction coefficient (LPC) that is a typical parameter set in speech coding. In this paper, we propose a speech coder using MFCC instead of LPC to improve the performance of a server-based speech recognition system in network environments. However, the main drawback of using MFCC is to develop the efficient MFCC quantization with a low-bit rate. First, we explore the interframe correlation of MFCCs, which results in the predictive quantization of MFCC. Second, a safety-net scheme is proposed to make the MFCC-based speech coder robust to channel error. As a result, we propose a 8.7 kbps MFCC-based CELP coder. It is shown from a PESQ test that the proposed speech coder has a comparable speech quality to 8 kbps G.729 while it is shown that the performance of speech recognition using the proposed speech coder is better than that using G.729.

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BS-PLC(Both Side-Packet Loss Concealment) for CELP Coder (CELP 부호화기를 위한 양방향 패킷 손실 은닉 알고리즘)

  • Lee In-Sung;Hwang Jeong-Joon;Jeong Gyu-Hyeok
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.42 no.12
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    • pp.127-134
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    • 2005
  • Lost packet robustness is an most important quality measure for voice over IP networks(VoIP). Recovery of the lost packet from the received information is crucial to realize this robustness. So, this paper proposes the lost packet recovery method from the received information for real-time communication for CELP coder. The proposed BS-PLC (Both Side Packet Loss Concealment) based WSOLA(Waveform Shift OverLab Add) allow the lost packet to be recovered from both the 'previous' and 'next' good packet as the LP parameter and the excitation signal are respectively recovered. The burst of packet loss is modeled by Gilbert model. The proposed scheme is applied to G.729 most used in VoIP and is evaluated through the SNR(signal to noise) and the MOS(Mean Opinion Score) test. As a simulation result, The proposed scheme provide 0.3 higher in Mean Opinion Score and 2 dB higher in terms of SNR than an error concealment procedure in the decoder of G.729 at $20\%$ average packet loss rate.

A Study on a Design of the Variable Bit-Rate Vocoder by Measuring of the Speaking Rate (발성 속도에 따른 가변전송률 CELP 부호화기 설계에 관한 연구)

  • 나덕수;배명진
    • Proceedings of the IEEK Conference
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    • 2001.06d
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    • pp.273-276
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    • 2001
  • CELP 부호화기는 선형 예측 합성에 의한 분석 부호화의 원칙에 기본을 두고 있다. 그리고 음성 신호의 스펙트럼을 LPC 분석을 통해 부호화하는데 고정 윈도우를 사용하여 부호화한다. 그러나 음성신호는 화자의 발성속도에 따라 파형의 변화가 시간적으로 빠르게 변화하기도 하고, 반대로 유사한 파형이 일정시간 유지되기도 한다. 따라서 윈도우의 크기를 발성속도에 맞추어 분석한다면 보다 효율적인 부호화를 할 수 있다. 본 논문에서는 발성속도에 따라 전송률을 달리 적용하는 방법을 제안한다. 발성속도의 측정은 스펙트럼 변화도를 이용하여 측정하였고, 발성속도가 빠를 때는 프레임 크기를 줄여 시간적으로 빠르게 변화하는 신호에 적응적으로 분석하고 대신 파라미터 표현에 비트를 줄인다. 반대로 발성속도가 느릴 때는 프레임 크기를 키우고 파라미터 표현에 비트를 더 할당한다. 제안한 방법을 실험하기 위해 G.723.1 5.3kbps ACELP 부호화기를 이용하였다 음질의 열하 없이 평균 16.34% 전송률 감소효과를 얻을 수 있었다.

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Tandemless Transcoding for AMR and EVRC Speech Coders (AMR과 EVRC 음성 부호화기간의 비탠덤 방식을 이용한 상호 부호화)

  • 이선일;유창동
    • The Journal of the Acoustical Society of Korea
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    • v.21 no.6
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    • pp.531-542
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    • 2002
  • Novel tandemless transcoding method for AMR and EVRC speech coders is proposed in this paper. In contrast to conventional tandem method, the parameters which is used commonly in speech coder where CELP algorithm is adapted are directly transcoded. The proposed algorithm is composed of LSP transcoding, pitch delay transcoding, gains transcoding and fixed codebook vector transcoding Evaluation results show that the novel algorithm achieves better speech quality than tandem method and reduce computational complexity and delay.