本論文主要以研究網路音訊之低位元率ITU-T G.723.1和G.729語音編碼器之實現為主。我們分別針對兩者隨機碼簿之搜尋部分進行計算量之簡化。在G.723.1編碼器中有5.3 kbps和6.3 kbps兩種位元率，隨機碼簿中分別採用MTP-ACELP和CMP-MLQ的方式來取代原本的ACELP和MP-MLQ。在G.729編碼器之隨機碼簿中，則是利用交相關函數d來預選搜尋以降低搜尋迴圈數同時我們亦提出簡化自相關函數Φ之計算方法。

The main research of the thesis is focused on the ITU-T G.729 and G.723.1 speech coder, which are low bit-rate speech coders used in digital networks. We propose some fast methods to reduce the complexity of G.729 and G.723.1 stochastic codebook searches. The MTP-ACELP and CMP-MLQ are suggested to improve the speed of ACELP and MP-MLQ search mechanisms in the G.723.1 coder. In the G.729 coder, the cross-correlation function d is used to reduce the search loops. Furthermore, we also propose some methods to reduce the complexity in computation of auto-correlation functionΦ.

[1] Juin-Hwey Chen, Richard V. Cox, Yen-Chen Lin, Nikil Jayant, and Melvin J. Melchner, “A low-delay” CELP Coder for the CCITT 16 kbit/s Speech Coding Standard”, IEEE Journal on Selected Areas in Communications, Vol.10, No.2, pp.830-849, June 1992.
[2] Joseph P. Campbell Jr., Vanoy C. Welch, Thomas E. Tremain, “An Expandable Error-Protected 4800 bps CELP Coder (US Federal Standard 4800 bps Voice Coder)”, IEEE Conference, pp.735-738, 1989.
[3] ITU-T Recommendation G.729, Coding of Speech at 8 kbit/s Using Conjugate-Structure Algebraic-Code-Excited Linear Prediction (CS-ACELP), March 1996.
[4] ITU-T Recommendation G.723.1, Dual Rate Speech Coder for Multimedia Communication Transmitting at 5.3 and 6.3 kbit/s, March 1996.
[5] ITU-T Recommendation G.729-Annex A: Reduced Complexity 8 kbit/s CS-ACELP Speech Coding Algorithm, March 1996.
[6] ITU-T Recommendation G.729-Annex E: 11.8 kbit/s CS-ACELP Speech Coding Algorithm, September 1998.
[7] ITU-T Recommendation G.729-Annex D: 6.4 kbit/s CS-ACELP Speech Coding Algorithm, September 1998.
[8] M. A. Ramirez and M. Gerken, “A Multistage Search of Algebraic CELP Codebooks”, Acoustics, Speech, and Signal Processing, Proceedings of IEEE International Conference, Vol.1, pp. 17-20,1999.
[9] M. A. Ramirez and M. Gerken, “Efficient Algebraic Multipulse Search”, ITS '98 Proceedings, SBT/IEEE International Telecommunications Symposium, Vol. 1, pp. 231-236, 1998.
[10] N. K. Ha, “A Fast Search Method of Algebraic Codebook by Reordering Search Sequence”, Acoustics, Speech, and Signal Processing, Proceedings of IEEE International Conference, Vol. 1, pp. 21-24, 1999.
[11] S. Singhal and B. S. Atal, “Amplitude Optimization and Pitch Prediction in Multipulse Coders” IEEE Transactions on Acoustics, Speech and Signal Processing, Vol.373, pp. 317-327, March 1989.
[12] Akitoshi Amada, Takehiro Moriya, and Dhinji Hayashi, “An 8 kbit/s Conjugate Structure CELP (CS-CELP) Speech Coder”, IEEE Transaction Speech and Audio Processing, Vol.4, No.6, pp.401-411, November 1996.
[13] ETSI, Digital Cellular Telecommunications System (Phase 2): Enhanced Full Rate (EFR) Speech Transcoding (GSM 06.60 version 6.0.0), ETSI EN 300 726, 1997
[14] R. Salami, C. Laflamme, B. Bessette and J-P. Adoul, “Description of GSM Enhanced Full Rate Speech Codec”, ICC '97 Montreal, Towards the Knowledge Millennium, IEEE International Conference, Vol. 2, pp. 725-729, 1997.
[15] ETSI, Digital Cellular Telecommunications System (Phase 2+): Half Rate Speech Transcoding (GSM 06.20 version 5.1.1), ETSI 300 969, May 1998.
[16] ISO/IEC 14496-3, Information technology – very low bitrate audio-visual coding, Part 3: Audio, Subpart 1-3, March 1998.
[17] S. Singhal and B. S. Atal, “Amplitude Optimization and Pitch Prediction in Multipulse Coders” IEEE Transactions on Acoustics, Speech and Signal Processing, Vol.373, pp. 317-327, March 1989.
[18] F. Beritelli, S. Casale and A. L. Corte, “A New Efficient Approach to the Optimization of a Low-Complexity Multipulse Speech Coder” Singapore ICCS '94. Conference Proceedings, Vol.3, pp. 888-892, 1994.
[19] F. K. Chen, J. F. Yang and Y. P. Lin, "Complexity Scalability for ACELP and MP-MLQ speech coders", IEICE Trans. Information and Systems, Apr. 2001.