1、 333 International Telecommunication Union ITU-T G.728TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2012) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital terminal equipments Coding of voice and audio signals Coding of speech at 16 kbit/s using low-delay code exci
2、ted linear prediction Recommendation ITU-T G.728 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL C
3、HARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499
4、TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 General G.700G.709 Coding of voice and audio signals G.710G.729Principal characteristics of primary multiplex equipment G.730G.739 Principal characteristics of second order multiplex equipment G.
5、740G.749 Principal characteristics of higher order multiplex equipment G.750G.759 Principal characteristics of transcoder and digital multiplication equipment G.760G.769 Operations, administration and maintenance features of transmission equipment G.770G.779 Principal characteristics of multiplexing
6、 equipment for the synchronous digital hierarchy G.780G.789 Other terminal equipment G.790G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTI
7、CS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.728 (06/2012) i Recommendation ITU-T G.728 Coding of speech at 16 kbit/s using
8、 low-delay code excited linear prediction Summary Recommendation ITU-T G.728 contains the description of an algorithm for the coding of speech signals at 16 kbit/s using low-delay code excited linear prediction (LD-CELP). The main description is found in the main body of the Recommendation, where th
9、e floating-point implementation of LD-CELP is described. Annexes A, B, C and D contain tables of constants used by the LD-CELP algorithm. In Annex E, the sequencing of variable adaptation and its use is given and Annex F lists the abbreviations used in this Recommendation. Annex G contains the alter
10、native16 kbit/s (16-bit) fixed-point specification of ITU-T G.728. The purpose of this Annex is to describe in sufficient detail how ITU-T G.728 operating at 16 kbit/s can be implemented on a fixed-point arithmetic device. A fixed-point implementation based on this description should be capable of f
11、ully interworking with a floating-point version of ITU-T G.728 and producing an output signal of equivalent quality, whether that signal is speech or an in-band data signal. ITU-T G.728 LD-CELP can operate at three bitrates other than 16 kbit/s, as defined in Annexes H and J. These additional operat
12、ing modes are particularly useful for applications such as digital circuit multiplication equipment (DCME). Annex H contains the modifications to ITU-T G.728 LD-CELP speech coding algorithm needed to reduce the coding bit rate down to 12.8 and 9.6 kbit/s. These modifications include the modification
13、s to the shape and gain codebooks. Operation at lower rates can assist DCME in handling increased voice traffic while showing a graceful quality degradation. Annex I is concerned with how to conceal the loss of bitstream information due to frame erasure or packet loss in the communications channel.
14、During normal operation, the decoder performs in a manner identical with the ITU-T G.728 main body or its Annex G when operating at 16 kbit/s, or with Annex H when operating at 12.8 or 9.6 kbit/s. The modification described in Annex I only involves changing the decoder during times when the bitstrea
15、m is unavailable. It is presumed that this loss of the bitstream is indicated to the decoder by some external means. Annex I is not essential for normal operation of ITU-T G.728. Annex J defines a 40 kbit/s extension that is optimized for voiceband data (VBD). The algorithmic delay is five samples l
16、ong (0.625 ms), which is the same as the other LD-CELP modes of operation described in this Recommendation. The 40 kbit/s VBD algorithm in Annex J is intended for VBD signal compression transmission in applications such as DCME. The algorithm allows soft transition to and from the other ITU-T G.728
17、LD-CELP operating modes, and is also designed to maintain toll-quality speech. Annex J is an implementation-efficient alternative to the 40 kbit/s ADPCM mode (ITU-T G.726) in DCME systems that incorporate LD-CELP (ITU-T G.728). Appendix I contains information on the implementation verification proce
18、dures for LD-CELP operating at 16 kbit/s (both floating- and fixed-point operation). This Appendix describes the digital test sequences and the measurement software to be used for implementation verification of ITU-T G.728. Provision is included for both floating-point implementations, based on the
19、ITU-T G.728 main body, and bit-exact fixed-point implementations, based on Annex G. Appendix II gives a broad outline of the speech performance of the 16 kbit/s LD-CELP algorithm when interacting with other parts of the network. Some general guidance is also offered on voice-like and non-voice signa
20、ls. The performance of ITU-T G.728 is compared to that of 32 kbit/s operating mode of the ITU-T G.726 ADPCM) and of ITU-T G.711 (64 kbit/s PCM). ii Rec. ITU-T G.728 (06/2012) Appendix III provides information on the operation of the algorithm defined in Annex I when frame erasures occur. This Recomm
21、endation includes an electronic attachment containing programs and test sequences for verification of the floating point and fixed point implementations of the ITU-T G.728 LD-CELP algorithm. History Edition Recommendation Approval Study Group 1.0 ITU-T G.728 1992-09-01 1.1 ITU-T G.728 Annex G 1994-1
22、1-01 15 1.2 ITU-T G.728 App. I Software 1995-07-01 1.3 ITU-T G.728 App. II 1995-11-13 1.4 ITU-T G.728 Annex H 1997-07-11 16 1.5 ITU-T G.728 Annex H 1999-05-27 16 1.6 ITU-T G.728 Annex I 1999-05-27 16 1.7 ITU-T G.728 Annex J 1999-09-30 16 1.8 ITU-T G.728 Annex G (1994) Cor. 1 2000-02-17 16 1.9 ITU-T
23、G.728 (1992) Amd. 1 2006-05-29 16 2.0 ITU-T G.728 2012-06-29 16 Rec. ITU-T G.728 (06/2012) iii FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunic
24、ation Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly
25、 (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which f
26、all within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this
27、Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory languag
28、e such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Rec
29、ommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of a
30、pproval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB p
31、atent database at http:/www.itu.int/ITU-T/ipr/. ITU 2013 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. iv Rec. ITU-T G.728 (06/2012) Table of Contents Page 1 Introduction and references 1 1.1 Introduction 1 1
32、.2 References 1 2 Outline of LD-CELP 1 2.1 LD-CELP encoder 2 2.2 LD-CELP decoder 2 3 LD-CELP (encoder principles) . 4 3.1 Input PCM format conversion 4 3.2 Vector buffer 5 3.3 Adapter for perceptual weighting filter 5 3.4 Perceptual weighting filter . 9 3.5 Synthesis filter 9 3.6 VQ target vector co
33、mputation 9 3.7 Backward synthesis filter adapter . 9 3.8 Backward vector gain adapter 11 3.9 Codebook search module . 13 3.10 Simulated decoder 16 3.11 Synchronization and in-band signalling . 16 4 LD-CELP decoder principles . 17 4.1 Excitation VQ codebook 17 4.2 Gain scaling unit . 18 4.3 Synthesi
34、s filter 18 4.4 Backward vector gain adapter 18 4.5 Backward synthesis filter adapter . 18 4.6 Postfilter . 18 4.7 Postfilter adapter . 20 4.8 Output PCM format conversion . 23 5 Computational details . 23 5.1 Description of basic coder parameters . 23 5.2 Description of internal variables 23 5.3 In
35、put PCM format conversion (block 1) 28 5.4 Vector buffer (block 2) . 28 5.5 Adapter for perceptual weighting filter (block 3, Figure 4-a) 28 5.6 Backward synthesis filter adapter (block 23, Figure 5) 30 5.7 Backward vector gain adapter (block 20, Figure 6) 32 5.8 Perceptual weighting filter . 35 5.9
36、 Computation of zero-input response vector . 36 5.10 VQ target vector computation 37 Rec. ITU-T G.728 (06/2012) v Page 5.11 Codebook search module (block 24) 37 5.12 Simulated decoder (block 8) . 40 5.13 Filter memory update for blocks 9 and 10 41 5.14 Decoder (Figure 3) . 42 Annex A Hybrid window f
37、unctions for various LPC analyses in LD-CELP . 51 A.1 Hybrid window for the synthesis filter . 51 A.2 Hybrid window for the log-gain predictor 52 A.3 Hybrid window for the perceptual weighting filter 53 Annex B Excitation shape and gain codebook tables . 55 Annex C Values for bandwidth broadcasting
38、. 59 Annex D Coefficients of the 1 kHz lowpass elliptic filter used in pitch period extraction module (block 82) 61 Annex E Time scheduling the sequence of computations 62 Annex F Alphabetical list of abbreviations used in this Recommendation 64 Annex G 16 kbit/s fixed point specification . 65 G.1 I
39、ntroduction 65 G.2 Algorithmic changes . 72 G.3 Pseudo-code for other modules of ITU-T G.728 81 G.4 LD-CELP internal variable representations . 117 G.5 Log-gain tables for gain and shape codebook vectors 121 G.6 Integer values of gain codebook related arrays 122 G.7 Encoder and decoder main program
40、pseudo-codes 123 Annex H Variable bit rate LD-CELP operation mainly for DCME at rates less than 16 kbit/s 126 H.1 Introduction 126 H.2 Principles of operation 126 H.3 Modifications for 12.8 kbit/s operation 127 H.4 Modifications for 9.6 kbit/s operation 131 Annex I Frame or packet loss concealment f
41、or the LD-CELP decoder 137 I.1 Scope 137 I.2 Normative references 137 I.3 Introduction 137 I.4 Principles of operation 138 I.5 Pseudo-code for frame erasure concealment 141 I.6 Additional coder parameters and variables 153 Annex J Variable bit-rate operation of LD-CELP mainly for voiceband-data appl
42、ications in DCME 155 J.1 Scope 155 J.2 Normative references 155 vi Rec. ITU-T G.728 (06/2012) Page J.3 Overview 155 J.4 Algorithm description . 156 Appendix I Programs and test sequences for implementation verification of the algorithm of the ITU-T G.728 16 kbit/s LD-CELP speech coder 186 I.1 Genera
43、l . 186 I.2 Test configurations . 186 I.3 Verification programs . 189 I.4 Test sequences 190 I.5 Verification tools distribution . 192 Appendix II Speech performance . 197 II.1 Introduction 197 II.2 Speech performance . 197 II.3 Performance with non-speech signals 198 II.4 Artificial voice signals 1
44、98 Appendix III Values used for scaling ETPAST during frame erasures 200 Bibliography. 201 Electronic attachment: Programs and test sequences for verification of the floating point and fixed point implementations of the ITU-T G.728 LD-CELP algorithm Rec. ITU-T G.728 (06/2012) 1 Recommendation ITU-T
45、G.728 Coding of speech at 16 kbit/s using low-delay code excited linear prediction 1 Introduction and references 1.1 Introduction This Recommendation contains the description of an algorithm for the coding of speech signals at 16 kbit/s using low-delay code excited linear prediction (LD-CELP). This
46、Recommendation is organized as follows. In clause 2 a brief outline of the LD-CELP algorithm is given. In clauses 3 and 4, the LD-CELP encoder and LD-CELP decoder principles are discussed, respectively. In clause 5, the computational details pertaining to each functional algorithmic block are define
47、d. Annexes A, B, C and D contain tables of constants used by the LD-CELP algorithm. In Annex E the sequencing of variable adaptation and use is given. Finally, in Appendix I information is given on procedures applicable to the implementation verification of the algorithm. Under further study is the
48、future incorporation of three additional appendices (to be published separately) consisting of LD-CELP network aspects, LD-CELP fixed-point implementation description, and LD-CELP fixed-point verification procedures. 1.2 References The following ITU-T Recommendations and other references contain pro
49、visions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The r
