1、 International Telecommunication Union ITU-T G.718TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2008) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital terminal equipments Coding of voice and audio signals Frame error robust narrow-band and wideband embedded variab
2、le bit-rate coding of speech and audio from 8-32 kbit/s Recommendation ITU-T G.718 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-TRANSMISSI
3、ON SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS 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 RADIOTELEPH
4、ONY AND LINE TELEPHONY G.450G.499 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.729 Principal characteristics of primary multiplex equipment G.730G.739 Principal characteristics of
5、second order multiplex equipment G.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 Princi
6、pal characteristics of multiplexing 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.19
7、99 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.718 (06/2008) i Recommendation ITU-T G.718 F
8、rame error robust narrow-band and wideband embedded variable bit-rate coding of speech and audio from 8-32 kbit/s Summary Recommendation ITU-T G.718 describes a narrow-band (NB) and wideband (WB) embedded variable bit-rate coding algorithm for speech and audio operating in the range from 8 to 32 kbi
9、t/s which is designed to be robust to frame erasures. This codec provides state-of-the-art NB speech quality over the lower bit rates and state-of-the-art WB speech quality over the complete range of bit rates. In addition, the ITU-T G.718 codec is designed to be highly robust to frame erasures, the
10、reby enhancing the speech quality when used in IP transport applications on fixed, wireless and mobile networks. Despite its embedded nature, the codec also performs well with both NB and WB generic audio signals. This codec has an embedded scalable structure, enabling maximum flexibility in the tra
11、nsport of voice packets through IP networks of today and in future media-aware networks. In addition, the embedded structure of ITU-T G.718 will easily allow the codec to be extended to provide a super-wideband and stereo capability through additional layers which are currently under development. Th
12、e bitstream may be truncated at the decoder side or by any component of the communication system to instantaneously adjust the bit rate to the desired value without the need for out-of-band signalling. The encoder produces an embedded bitstream structured in five layers corresponding to the five ava
13、ilable bit rates: 8, 12, 16, 24 and 32 kbit/s. The ITU-T G.718 encoder can accept WB sampled signals at 16 kHz, or NB signals sampled at either 16 or 8 kHz. Similarly, the decoder output can be 16 kHz WB, in addition to 16 or 8 kHz NB. Input signals sampled at 16 kHz, but with bandwidth limited to N
14、B, are detected by the encoder. The output of the ITU-T G.718 codec is capable of operating with a bandwidth of 300-3400 Hz at 8 and 12 kbit/s and 50-7000 Hz from 8 to 32 kbit/s. The high quality codec core represents a significant performance improvement, providing 8 kbit/s wideband clean speech qu
15、ality equivalent to the ITU-T G.722.2 codec at 12.65 kbit/s whilst the 8 kbit/s narrow-band codec operating mode provides clean speech quality equivalent to the ITU-T G.729E codec at 11.8 kbit/s. The codec operates on 20-ms frames and has a maximum algorithmic delay of 42.875 ms for wideband input a
16、nd wideband output signals. The maximum algorithmic delay for narrow-band input and narrow-band output signals is 43.875 ms. The codec may also be employed in a low-delay mode when the encoder and decoder maximum bit rates are set to 12 kbit/s. In this case, the maximum algorithmic delay is reduced
17、by 10 ms. The codec also incorporates an alternate coding mode, with a minimum bit rate of 12.65 kbit/s, which is bitstream interoperable with Recommendation ITU-T G.722.2, 3GPP AMR-WB and 3GPP2 VMR-WB mobile WB speech coding standards. This option replaces layer 1 and layer 2, and the layers 3-5 ar
18、e similar to the default option with the exception that in layer 3 fewer bits are used to compensate for the extra bits of the 12.65 kbit/s core. The decoder is further able to decode all other ITU-T G.722.2 operating modes. Furthermore, a new annex to this Recommendation is under development that w
19、ill efficiently enable bit-stream interoperability with the 3GPP2 EVRC-WB codec. This Recommendation also includes discontinuous transmission mode (DTX) and comfort noise generation (CNG) algorithms that enable bandwidth savings during inactive periods. An integrated noise reduction algorithm can be
20、 used provided that the communication session is limited to 12 kbit/s. ii Rec. ITU-T G.718 (06/2008) The underlying algorithm is based on a two-stage coding structure: the lower two layers are based on code-excited linear prediction (CELP) coding of the band (50-6400 Hz) where the core layer takes a
21、dvantage of signal classification to use optimized coding modes for each frame. The higher layers encode the weighted error signal from the lower layers using overlap-add modified discrete cosine transformation (MDCT) transform coding. Several technologies are used to encode the MDCT coefficients to
22、 maximize performance for both speech and music. Corrigendum 1 (11/2008) corrects a number of minor problems that have been identified in the fixed-point ANSI C source code of the base text of this Recommendation. Amendment 1 (03/2009) introduces some additional minor corrections to the fixed-point
23、ANSI C source code and to the text of the Recommendation. It also describes an addition of a verification of the default value of the layer 5 unused bit, and the procedure of erasure of layer 5 if the bit does not have the default value. Amendment 1 also introduces the new Annex A, which defines an
24、alternative implementation of the ITU-T G.718 algorithm using floating point arithmetic to be used for implementation on DSP hardware optimized for floating-point operations. The accompanying floating point ANSI C source code is fully interoperable with the fixed-point code. While Corrigendum 2 (08/
25、2009) includes further corrections to address minor problems found in both the fixed and floating-point implementations, its main benefit is in the streamlining of the fixed-point implementation which reduces the complexity of the codec from 69 to 57 WMOPS whilst remaining bit-exact with the origina
26、l code on both steps of the characterization text. This 17% complexity reduction is significant and will clearly make the G.718 more attractive to implement. This Recommendation contains an electronic attachment with the ANSI C source code, which is an integral part of this Recommendation. This edit
27、ion integrates all changes introduced by Corrigendum 1 (11/2008), Amendment 1 (03/2009) and Corrigendum 2 (08/2009), including the associated updated ANSI C source code. Source Recommendation ITU-T G.718 was approved on 16 June 2008 by ITU-T Study Group 16 (2005-2008) under Recommendation ITU-T A.8
28、procedure. This edition includes Corrigendum 1 approved on 13 November 2008, Amendment 1 approved on 16 March 2009 and Corrigendum 2 approved on 29 August 2009 by ITU-T Study Group 16 (2009-2012) under Recommendation ITU-T A.8 procedures. Rec. ITU-T G.718 (06/2008) iii FOREWORD The International Tel
29、ecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and
30、tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Rec
31、ommendations 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 fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recom
32、mendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperab
33、ility or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that com
34、pliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validi
35、ty 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 approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required t
36、o implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2009 All rights reserved. No part of this publication may be reproduced, by
37、 any means whatsoever, without the prior written permission of ITU. iv Rec. ITU-T G.718 (06/2008) CONTENTS Page 1 Scope 1 2 References. 1 3 Abbreviations and acronyms 1 4 Mathematical expressions. 3 5 General description of the coder. 3 5.1 Input/output sampling rate 4 5.2 Codec delay 4 5.3 DTX/CNG
38、operation 5 5.4 Optional noise reduction. 5 5.5 ITU-T G.722.2-interoperable option 5 5.6 Complexity and memory 5 5.7 Coder description 6 5.8 Organization of the rest of this Recommendation 7 6 Functional description of the encoder. 7 6.1 Common processing . 9 6.2 Signal activity detection . 15 6.3 N
39、oise reduction aspects 16 6.4 Linear prediction analysis. 21 6.5 Perceptual weighting 25 6.6 Open-loop pitch analysis 26 6.7 Noise energy estimation . 32 6.8 Classification-based core layer (layer 1) 42 6.9 Embedded ACELP enhancement layer (layer 2) 99 6.10 Frame erasure concealment side information
40、 (layer 3) 109 6.11 Transform coding of higher layers (layers 3, 4, 5). 111 6.12 DTX/CNG operation 160 6.13 ITU-T G.722.2-interoperable option 165 7 Functional description of the decoder. 170 7.1 Core layer decoding (layer 1). 171 7.2 Embedded ACELP enhancement layer decoding (layer 2) 179 7.3 Synth
41、esis. 181 7.4 NB post-processing 182 7.5 De-emphasis . 185 7.6 Resampling from 12.8 kHz to the output sampling frequency. 185 7.7 NB music enhancer. 187 7.8 Reconstruction of the high-frequency band for WB output . 194 7.9 Decoding of frame erasure concealment side information (layer 3) 196 7.10 Hig
42、her layer transform decoding (layers 3, 4, 5) 196 Rec. ITU-T G.718 (06/2008) v Page 7.11 Frame erasure concealment 204 7.12 Decoding in DTX/CNG operation 224 7.13 Decoding in ITU-T G.722.2-interoperable option . 225 7.14 Common post-processing . 229 8 Description of the transmitted parameter indices
43、 . 234 8.1 Bit allocation for the default option 234 8.2 Bit allocation for SID frames in the DTX operation 239 8.3 Bit allocation for the ITU-T G.722.2-interoperable option 239 9 Bit-exact description of the ITU-T G.718 coder 240 9.1 Use of the simulation software. 240 9.2 Organization of the simul
44、ation software 242 Annex A Reference floating-point implementation for ITU-T G.718 243 A.1 Scope 243 A.2 References 243 A.3 Overview 243 A.4 Algorithmic description 243 A.5 ANSI C-code 243 Bibliography. 245 Electronic attachment: ANSI C source code Rec. ITU-T G.718 (06/2008) 1 Recommendation ITU-T G
45、.718 Frame error robust narrow-band and wideband embedded variable bit-rate coding of speech and audio from 8-32 kbit/s11 Scope This Recommendation contains the description of an algorithm for the scalable coding of narrow-band and wideband speech and audio signals at 8-32 kbit/s. This Recommendatio
46、n is organized as follows. The references and abbreviations used throughout this Recommendation are defined in clauses 2 and 3, respectively. Clause 5 gives a general outline of the ITU-T G.718 algorithm. The ITU-T G.718 encoder and decoder principles are discussed in clauses 6 and 7, respectively.
47、The transmitted parameters are presented in clause 8. Clause 9 describes the software that defines this coder in 16-32 bits fixed-point arithmetic. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of
48、 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 o
49、ther references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.191 Recommendation ITU-T G.191 (2005), Software tools for speech and audio coding standardization. ITU-T G.192 Recommendation ITU-T G.192 (1996), A common digital parallel interface for speech standardization activities. ITU-T G.722.2 Recommendation ITU-T G.722.2 (2003), Wideband coding of speech at around 16 kb
