• Title/Summary/Keyword: CELP

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Implementation of MPEG4-CELP Vocoder for Speech Codec of Internet Video Phone (인터넷 화상 전화용 음성 코텍을 위한 MPEG4-CELP 부호화기의 구현)

  • 김병수;김동형;강경옥;홍진우;정재호
    • Proceedings of the IEEK Conference
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    • 2000.09a
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    • pp.119-122
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    • 2000
  • 인터넷이 일상생활에 다양하게 활용되면서 인터넷 채널을 통한 정보의 형태는 문자와 이미지 외에 음성, 오디오 신호 및 동영상 부분까지 확대되고 있다. 본 논문에서는 MPEG4-CELP를 인터넷 화상 통신의 음성 코덱용으로 사용하기 위한 최적화 기법 및 알고리듬의 개선을, DSP칩이 내장된 보드가 아닌 인터넷의 터미널로 사용되고 있는 펜티엄 프로세서를 장착한 PC에 초점을 맞추어 수행하였다. MPEG4-CELP VM C소스를 분석 및 프로파일(Profile)한 결과를 토대로 패라미터 추출을 위해 많은 연산을 수행하는 부호화기에 대해서 CPU상에 부하를 많이 주는 함수들을 제 1차 최적화 대상 함수들로 선정하고, CPU에 부하를 많이 주지는 않으나 호출되는 회수가 많은 함수를 2차 최적화 대상 함수로 선정해, C소스 레벨의 소프트웨어 파이프 라이닝(Software Pipelinging) 기법들을 적용하여 최적화를 수행하였다. 또한 1차 최적화 대상 함수의 경우에는 소프트웨어 파이프라이닝의 적용과 함께 연산량 감소를 위한 알고리듬 변형까지 수행하였다. 위의 과정을 거쳐 최적화 된 MPEG4-CELP는 펜티엄Ⅲ 450㎒ PC에서 음성을 부호화 하는데 원 VM소스에 비해 약 2배정도의 시간이 단축되는 것을 확인하였다.

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A region-adaptive CELP image coder for still images at low bit rates (낮은 비트율에서 정지 영상 코딩을 위한 영역 적응 CELP 부호화기)

  • 박용철;차인환;윤대희
    • Journal of the Korean Institute of Telematics and Electronics B
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    • v.32B no.12
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    • pp.1614-1623
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    • 1995
  • In this paper we propose a region-adaptive CELP image coder for still images at low bit rates below 0.5 bpp. The proposed method partitions the image into stochastically similar regions by the minimum spanning tree method and finds prediction coefficients for each region using a 2- dimensional linear prediction model. Coding is carried out on 8$\times$8 blocks and when there are several regions included in a block, an image is synthesized using the prediction coefficients of each region. Computer simulation results show that the proposed method allows improved synthesized image over conventional block-adaptive CELP methods, especially at edges. In addition, performance comparison with the JPEG DCT method shows that while the JPEG method shows block distortion and staircase effects (ragged edges) at bit rates below 0.5 bpp, the proposed CELP method shows improved synthesized images with such effects reduced.

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On a Reduction of Pitch Searching Time by Preliminary Pitch in the CELP Vocoder

  • Bae, Seong-Gyun;Kim, Hyung-Rae;Kim, Dae-Sik;Bae, Myung-Jin
    • Proceedings of the Acoustical Society of Korea Conference
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    • 1994.06a
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    • pp.1104-1111
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    • 1994
  • Code Excited Linear Prediction(CELP) as a speech coder exhibits good performance at data rates below 4.8 kbps. The major drawback to CELP type coders is their large amount of computation. In this paper, we propose a new pitch search method that preserves the quality of the CELP vocoder with reduced complexity. The basic idea is to restrict the pitch searching range by estimating the preliminary pitches. Applying the proposed method to the CELP vocoder, we can get approximately 87% complexity reduction in the pitch search.

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Spectrum Representation Based on LPC Cepstral VQ for Low Bit Rate CELP Coder (LPC Cepstral 벡터 양자화에 의한 저 전송율 CELP 음성부호기의 스펙트럼 표기)

  • 정재호
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.19 no.4
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    • pp.761-771
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    • 1994
  • This paper focuses on how spectrum information can be represented efficiently in a very low bit rate CELP speech coder. To achieve the goal, an LPC cepstral coefficients VQ scheme representing the spectrum information in a CELP coder is proposed. To represent the spectrum information using LPC cepstrums, three different cepstral distance measures having different spectral meanings in the frequency domain are considered, and their performances are compared and analyzed. The experimental results show that spectrum information in low bit rate CELP coders can be represented very efficiently using the proposed LPC cepstral vector quantization scheme.

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Implementation of Real Time Multi-User Communication System with MPEG-4 CELP (MPEG-4 CELP를 이용한 실시간 다자간 통신시스템의 구현)

  • 김헌중;우광희;차형태
    • The Journal of the Acoustical Society of Korea
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    • v.19 no.3
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    • pp.57-62
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    • 2000
  • In recent, the innovative improvement of a internet and computing environment make users desire the capability of processing information in real time. In this paper we implement a PC-to-PC real time multi-user communication system on the internet environment using the efficient algorithm for a real time processing and the MFEG-4 CELP codec which can be used for a low bit-rate coding from 6 to 24kbps. The implemented system produces a compressed bit-streams with the MPEG-4 CEU Mode-I 18200bps mode. There is 5 frames for a package and 1 frame has 160 samples. We can use this system to communicate with 4 users simultaneously in real time. The system is designed and examined on the Windows operating system.

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A New Fast Pitch Search Algorithm using Line Spectrum Frequency in the CELP Vocoder (CELP보코더에서 Line Spectrum Frequency를 이용한 고속 피치검색)

  • Bae, Myung-Jin;Sohn, Sang-Mok;Yoo, Hah-Young;Byun, Kyung-Jin
    • The Journal of the Acoustical Society of Korea
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    • v.15 no.2
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    • pp.90-94
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    • 1996
  • Code Excited Linear Prediction(CELP) vocoder exhibits good performance at data rates below 8 kbps. The major drawback of CELP type coders is a large amount of computation. In this paper, we propose a new pitch searching method that preserves the quality of the CELP vocoder reducing computational complexity. The basic idea is that grasps preliminary pitches using the first formant of speech signal and performs pitch search only about the preliminary pitches. As applying the proposed method to the CELP vocoder, we can reduce complexity by 64% in the pitch search.

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A CELP Coder using the Band-Divided Long Term Prediction (대역 분할 장구간 예측을 이용한 CELP 부호화기)

  • Choi, Young-Soo;Kang, Hong-Goo;Lim, Myoung-Seob;Ahn, Dong-Soon;Youn, Dae-Hee
    • The Journal of the Acoustical Society of Korea
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    • v.14 no.4
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    • pp.38-45
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    • 1995
  • In this paper a way to improve the performance of the long term prediction is proposed, which adopts the Multi-band Excitation (MBE) method in addition to the Code-Excited Linear Prediction (CELP) method at low bit rates below 4.8 kbps. In the proposed method, the multiband long term prediction is performed on the periodic components which still remain after the long term prediction of the conventional CELP method. At this point, the whole frequency region is divided into subbands whose size is equal to the spacing between the harmonics of the fundamental frequency, and the periodic multiband excitation signals. are represented as the sum of sine waves approximately as large as the spectrum of the excitation signals, so that the actual characteristics of the excitation signals can be better taken into account. To evaluate the performance of the proposed method, computer simulation is performed at 4.8 kbps. The 4.8 kbps DoD CELP and the 4.4 kbps IMBE were chosen as the reference vocoders for the speech quality measure. The result of the perceptual speech quality measure showed that the performance of the proposed method is better than that of the 4.8 kbps DoD CELP vocoder, and similar to that of the 4.4 kbps IMBE vocoder.

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Design of a Variable Bit Rate Speech Coder Based on One-dimensional SPIHT (1차원 SPIHT를 이용한 가변 비트율 음성 부호기의 설계)

  • Na, Hoon;Jeong, Dae-Gwon
    • The Journal of the Acoustical Society of Korea
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    • v.22 no.6
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    • pp.443-451
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    • 2003
  • Since a codebook-based CELP coder models its excitation signal according to one of several bit rates pre-assigned to codebooks and synthesizes speech signal using codebooks, it can not support encoding of speech signal at an arbitrary bit rate in one encoder. The proposed variable bit rate speech coder encodes the excitation signal based on the bit rate assigned to a present frame of speech using one-dimensional SPIHT and wavelet transform. Also it does't need to model excitation signal (or codebook) to some types as CELP coder, and can encode excitation signal at various bit rates without exact pitch information according to user requirement. As a result, since the coder doesn't have a codebook structure, it has relatively low coder complexity and provides equal or better speech quality compared to G.729 and G.723.1 coder.

Reduced Search for a CELP Adaptive Codebook (CELP 부호화기의 코드북 탐색 시간 개선)

  • Lee, Ji-Woong;Na, Hoon;Jeong, Dae-Gwon
    • Journal of Advanced Navigation Technology
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    • v.4 no.1
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    • pp.67-77
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    • 2000
  • This paper proposes a reduction scheme for codebook search time in the adaptive codebook using wavelet transformed coefficients. In a CELP coder, pitch estimation with a combined open loop and closed loop search in adaptive codebook needs a lengthy search. More precisely, the pitch search using autocorrelation function over all possible ranges has been shown inefficient compared to the consuming time. In this paper, we propose a new adaptive codebook search algorithm which ensures the same position for the pitch with maximum wavelet coefficient over various scaling factors in Dyadic wavelet transform. A new adaptive codebook search algorithm reduces 25% conventional search time with almost the same quality of speech.

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