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研究生:江佩芳
研究生(外文):Pei-Fang Chiang
論文名稱:混合激發線性預測語音編碼之研究
論文名稱(外文):The Research of Mixed Excitation Linear Prediction ( MELP ) Speech Coding
指導教授:廖德祿
指導教授(外文):Teh-Lu Liao
學位類別:碩士
校院名稱:國立成功大學
系所名稱:工程科學系碩博士班
學門:工程學門
學類:綜合工程學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:英文
論文頁數:66
中文關鍵詞:語音編碼
外文關鍵詞:MELPspeech coding
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語音編碼不論是在資料壓縮或是語音的傳輸上都極為重要,而語音傳輸是目前最主要也最普遍的通訊傳輸服務。儘管語音編碼技術很早就發展出來,但是隨著科技的發展依舊不斷的推陳出新。新的語音編碼傳輸位元率已由8Kbps(CELP)與4.8Kbps(CS-ACELP)發展至2.4Kbps(MELP)。也因為傳輸位元率的降低,語音品質就只能由更複雜的演算法來提升,這使得實現快速語音編碼相當困難。
繼FS1016 CELP 4.8K bps之後, 美國國防部於1996年宣佈了混合激發線性預測編碼器(MELP),為2.4K bps語音編碼的新標準,其目的是在傳輸網路頻寬限制下,藉由壓縮後資料的傳送,來節省傳輸位元率,並在解碼端能迅速還原音質良好的聲音訊號。
因此本論文也特別針對MELP語音編碼器架構之各單元作一介紹。並著手於程式的撰寫,程式部分是以C語言來實現,且列舉幾個例子來比較合成語音與原始語音的差異,結果驗證合成語音與原始語音以人耳辨識幾乎一樣。最後,提出語音壓縮系統未來之研究方向。
Speech coding is very important in data compression and speech communication. Speech communication is at present the most dominant and common service in telecommunication networks. Though, speech coding technology is well developed, science and technology still to find new ways of speech coding from old theories continuously. The transmission bit rate of new digital speech coding techniques has dropped from 8 Kbps (CELP), 4.8Kpbs (CS-ACELP) to 2.4 Kbps (MELP). As the bit rate decreasing, the speech quality can only be maintained by employing very complex algorithms which are difficult to implement in real time.
After FS1016 CELP 4.8K bps, the MELP vocoder was selected as the new 2400 bps Federal Standard speech coder by the United Stated Department of Defense Digital Voice Processing Consortium (DDVPC) in 1996. The purpose is in limited bandwidth of the transmission network by data transfer after compression, to economize bit rates, and to return to high quality of the original speech signal quickly in the decoder.
Hence, the units of MELP coder will be described in this thesis. The algorithm will be programmed in C language. We list several examples to compare the difference between the synthesized speech and the original speech. Experiments show that the synthesized speech sounds almost identical to the original speech. Finally, research direction in the future of speech compression system will be discussed.
Abstract in Chinese I
Abstract in English III
Acknowledgement V
Contents VI
List of Figures IX
List of Tables XI

Chapter 1 Introduction 1
1.1 Motivation 1
1.2 Organization 2
Chapter 2 Speech Coding 3
2.1 Coding Strategies 3
2.1.1 Waveform Coding 4
2.1.2 Parametric Coding 5
2.1.3 Hybrid Coding 5
2.2 LPC Basics 6
2.2.1 Linear Predictive Analysis 7
2.2.2 Solutions to LPC Analysisn 9
2.3 Pitch Prediction 13
2.4 Analysis-by Synthesis (AbS) Coding of Speech 14
2.5 Excitation Signal 15
2.6 Voice Compression Standards 16
Chapter 3 MELP Algorithm Description 17
3.1 MELP coder Introduction 17
3.2 Encoder 17
3.2.1 Low Frequency Remove 18
3.2.2 Pitch Calculation 18
3.2.3 LPC Analysis 25
3.2.4 Aperiodic Flag 26
3.2.5 Fourier Magnitude Calculation 26
3.2.6 Quantization 26
3.2.7 Error Protection And Bit Packing 33
3.2.8 Transmission Bit Stream 33
3.3 Decoder 34
3.3.1 Bit Unpacking and Error Correction 35
3.3.2 Noise Attenuation 38
3.3.3 Parameter Interpolation 39
3.3.4 Mixed Excitation Generation 40
3.3.5 Adaptive Spectral Enhancement 43
3.3.6 Linear Prediction Synthesis 44
3.3.7 Gain Adjustment 45
3.3.8 Pulse Dispersion 45
3.3.9 Synthesis Loop Control 45
Chapter 4 Implementation of MELP Vocoder and Results 46
4.1 Analog Specification 46
4.1.1 Format 46
4.1.2 Attributes 47
4.2 Implementation and Results 48
Chapter 5 Conclusions and Future Research Works 61
5.1 Conclusions 61
5.2 Future Research Works 61
References 63
Appendix 65
[1]A. M. Kondoz, “Digital speech :/coding for low bit rate communication systems”, J. Wiley, Chichester, 1994.
[2]Speech coding: http://cslu.cse.ogi.edu/HLTsurvey/ch10node4.html
[3]T.T. Teo, E.C. Tan,” Implementation of 2400 bps MELP vocoder on TMS320C44”, Signal Processing Proceedings, 1998. ICSP '98. 1998 Fourth International Conference on , 1998, pp. 576-579.
[4]T. E. Tremain, M. A. Kohler, T. G. Champion, “Philosophy and Goals of the DoD 2400 bps Vocoder Selection Process”, proceedings of ICASSP, IEEE, pp. 1137-1140,1996.
[5]MELP Vocoder Algorithm: http://www.aspi.com/tech/specs/pdfs/melp.pdf
[6]A. Nejat Ince, “Digital speech processing :/speech coding, synthesis, and recognition”, Kluwer Academic Publishers, Boston, 1992.
[7]Waveform Codecs: http://www-mobile.ecs.soton.ac.uk/speech_codecs/waveform.html
[8]MELP (Mixed Excitation Linear Prediction) Speech Coder: http://www.hait.ac.il/staff/commEng/Noam_Amir/speech/melp/contents.htm
[9]Source Codecs: http://www-mobile.ecs.soton.ac.uk/speech_codecs/source.html
[10]Hybrid Codecs: http://www-mobile.ecs.soton.ac.uk/speech_codecs/hybrid.html
[11]Lawrence R. Rabiner, Ronald W. Schafer, “Digital processing of speech signals”, Prentice-Hall, N.J., 1978.
[12]ITN530 Corporate Telecommunication, Voice Compression: http://sky.fit.qut.edu.au/~rolf/itn530/ass982/ang/voice.htm
[13]“Analog to Digital Conversion of Voice by 2400 Bit/second Mixed Excitation Linear Prediction (MELP)”, Draft FIBS Publication on MELP, May 28, 1998.
[14]Xiao Lin, Choon Boon Lim, Soo Peng Hoh, Gang Li, Hai Bin Huang, “Real time implementation of low bit rate speech encoder MELP on TMS320C54x DSP”, Signal Processing Proceedings, 2000. WCCC-ICSP 2000. 5th International Conference on , Volume: 2 , 2000, pp. 651-654.
[15]“Final Report for Fixed-Point and TMS320C5x Implementation of the 2.4 kbps MELP Federal Standard Speech Coder”, TI DSPS R&D Center, April 29, 1998.
[16]Teo Tse Tsong, Tan Eng Chong, “Real-Time Implementation of MELP Vocoder”.
[17]McCree, A.; Kwan Truong; George, E.B.; Barnwell, T.P.; Viswanathan, V., “An Enhanced 2.4 Kbit/s MELP Coder”, Speech Coding for Telecommunications, 1995. Proceedings., 1995 IEEE Workshop on, pp. 101-102.
[18]McCree, A.; Kwan Truong; George, E.B.; Barnwell, T.P.; Viswanathan, V., “A 2.4 kbit/s MELP coder candidate for the new U.S. Federal Standard”, Acoustics, Speech, and Signal Processing, 1996. ICASSP-96. Conference Proceedings., 1996 IEEE International Conference on , Volume: 1 , 1996, pp. 200-203.
[19]Supplee, L.M.; Cohn, R.P.; Collura, J.S.; McCree, A.V., “MELP: the new Federal Standard at 2400 bps”, Acoustics, Speech, and Signal Processing, 1997. ICASSP-97., 1997 IEEE International Conference on , Volume: 2 , 1997, pp. 1591-1594.
[20]A New Federal Standard Algorithm for 2400bps Coded Voice: http://maya.arcon.com/ddvpc/24results.htm
[21]MELP speech coding examples: http://www.ee.bilkent.edu.tr/~cetin/melp.html
[22]Speech Analysis http://svr-www.eng.cam.ac.uk/~ajr/SA95/
[23]Waveform Coding Techniques: http://www.cisco.com/warp/public/788/signalling/waveform_coding.html
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