1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T G.722.2TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Annex A(01/2002) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital terminal equipments Coding of analogue signals by methods other than PCM Wideband coding of speech at ar
2、ound 16 kbit/s using Adaptive Multi-Rate Wideband (AMR-WB) Annex A: Comfort noise aspects ITU-T Recommendation G.722.2 Annex A ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTI
3、CS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION 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
4、LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TESTING EQUIPMENTS G.500G.599 TRANSMISSION MEDIA CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 General G.700G.709 Coding of analogue signals by pulse code modulation G.710G.719 Coding of analogue signal
5、s by methods other than PCM G.720G.729 Principal characteristics of primary multiplex equipment G.730G.739 Principal characteristics of second order multiplex equipment G.740G.749 Principal characteristics of higher order multiplex equipment G.750G.759 Principal characteristics of transcoder and dig
6、ital multiplication equipment G.760G.769 Operations, administration and maintenance features of transmission equipment G.770G.779 Principal characteristics of multiplexing equipment for the synchronous digital hierarchy G.780G.789 Other terminal equipment G.790G.799 DIGITAL NETWORKS G.800G.899 DIGIT
7、AL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 QUALITY OF SERVICE AND PERFORMANCE G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 General G.6000G.6099 Symmetric cable pairs G.6100G.6199 Land coaxial cable pairs G.6200G.6299 Submarine cables G.6300G.6499 Optical fibre cables G.6500G.6599
8、 Characteristics of optical components and subsystems G.6600G.6999 DIGITAL TERMINAL EQUIPMENTS G.7000G.7999 General G.7000G.7099 Coding of analogue signals by pulse code modulation G.7100G.7199 Coding of analogue signals by methods other than PCM G.7200G.7299 Principal characteristics of primary mul
9、tiplex equipment G.7300G.7399 Principal characteristics of second order multiplex equipment G.7400G.7499 Principal characteristics of higher order multiplex equipment G.7500G.7599 Principal characteristics of transcoder and digital multiplication equipment G.7600G.7699 Operations, administration and
10、 maintenance features of transmission equipment G.7700G.7799 Principal characteristics of multiplexing equipment for the synchronous digital hierarchy G.7800G.7899 Other terminal equipment G.7900G.7999 DIGITAL NETWORKS G.8000G.8999 General aspects G.8000G.8099 Design objectives for digital networks
11、G.8100G.8199 Quality and availability targets G.8200G.8299 Network capabilities and functions G.8300G.8399 SDH network characteristics G.8400G.8499 Management of transport network G.8500G.8599 SDH radio and satellite systems integration G.8600G.8699 Optical transport networks G.8700G.8799 For furthe
12、r details, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.722.2/Annex A (01/2002) i ITU-T Recommendation G.722.2 Wideband coding of speech at around 16 kbit/s using Adaptive Multi-Rate Wideband (AMR-WB) Annex A Comfort noise aspects Summary This annex details the operation of the ba
13、ckground acoustic noise evaluation, noise parameter encoding/decoding and comfort noise generation for the AMR Wideband (AMR-WB) speech codec during Source Controlled Rate (SCR) operation. The comfort noise operations described here were also adopted by 3GPP in 3GPP specification TS 26.192. Source A
14、nnex A to ITU-T Recommendation G.722.2 was prepared by ITU-T Study Group 16 (2001-2004) and approved under the WTSA Resolution 1 procedure on 13 January 2002. ii ITU-T Rec. G.722.2/Annex A (01/2002) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in
15、the field of telecommunications. The ITU Telecommunication 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.
16、 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 Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resoluti
17、on 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 Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and
18、 a recognized operating agency. 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, validity or applicability of cla
19、imed 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 to implement this Recommend
20、ation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2002 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permissio
21、n of ITU. ITU-T Rec. G.722.2/Annex A (01/2002) iii CONTENTS Page A.1 Scope 1 A.2 Definitions, symbols and abbreviations . 1 A.2.1 Definitions 1 A.2.2 Symbols 1 A.2.3 Abbreviations . 2 A.3 General . 2 A.4 Functions on the transmit (TX) side. 2 A.4.1 ISF evaluation 3 A.4.2 Frame energy calculation . 4
22、 A.4.3 Analysis of the variation and stationarity of the background noise . 5 A.4.4 Modification of the speech encoding algorithm during SID frame generation. 5 A.4.5 SID-frame encoding . 6 A.5 Functions on the receive (RX) side 6 A.5.1 Averaging and decoding of the LP and energy parameters . 6 A.5.
23、2 Comfort noise generation and updating . 7 A.6 Computational details and bit allocation 7 ITU-T Rec. G.722.2/Annex A (01/2002) 1 ITU-T Recommendation G.722.2 Wideband coding of speech at around 16 kbit/s using Adaptive Multi-Rate Wideband (AMR-WB) Annex A Comfort noise aspects A.1 Scope This annex
24、details the operation of the background acoustic noise evaluation, noise parameter encoding/decoding and comfort noise generation for the AMR Wideband (AMR-WB) speech codec during Source Controlled Rate (SCR) operation. Implementation of this annex is necessary for interoperability with 3GPP systems
25、, but its use is not limited to mobile applications. The user should note however that the C-code implementation of this annex is available as part of the C-code in Annex C/G.722.2. In case of discrepancy between the requirements described in this annex and the fixed point computational description
26、of these requirements contained in Annex C/G.722.2, the description in Annex C/G.722.2 shall prevail. A.2 Definitions, symbols and abbreviations A.2.1 Definitions This annex defines the following terms: A.2.1.1 frame: Time interval of 20 ms corresponding to the time segmentation of the adaptive mult
27、i-rate wideband speech transcoder, also used as a short term for “traffic frame“. A.2.1.2 SID frames: Special Comfort Noise frames. It may convey information on the acoustic background noise or inform the decoder that it should start generating background noise. A.2.1.3 speech frame: Traffic frame t
28、hat cannot be classified as a SID frame. A.2.1.4 VAD flag: Voice Activity Detection flag. A.2.1.5 TX_TYPE: Classification of the transmitted traffic frame (defined in Annex B/G.722.2). A.2.1.6 RX_TYPE: Classification of the received traffic frame (defined in Annex B/G.722.2). Other definitions of te
29、rms used in this annex can be found in the main body of ITU-T Rec. G.722.2 and in Annex B/G.722.2. The overall operation of SCR is described in Annex B/G.722.2. A.2.2 Symbols This annex uses the following symbols. Boldface symbols are used for vector variables: fT= f1f2. f16 Unquantized ISF vector 1
30、621T.fff=f Quantized ISF vector f (m)Unquantized ISF vector of frame m )(mf Quantized ISF vector of frame m f meanAveraged ISF parameter vector enlogLogarithmic frame energy 2 ITU-T Rec. G.722.2/Annex A (01/2002) meanenlogAveraged logarithmic frame energy e ISF parameter prediction residual Quantize
31、d ISF parameter prediction residual =bannx )( = x(a) + x(a + 1) + . + x(b 1) + x(b) A.2.3 Abbreviations This annex uses the following abbreviations: AMR Adaptive Multi-Rate AMR-WB Adaptive Multi-Rate Wideband CN Comfort Noise ISF Immittance Spectral Frequency ISP Immittance Spectral Pair LP Linear P
32、rediction RSS Radio Subsystem RX Receive SCR Source Controlled Rate (operation) (aka source discontinuous transmission) SID Silence Insertion Descriptor TX Transmit UE User Equipment VAD Voice Activity Detector A.3 General A basic problem when using SCR is that the background acoustic noise, which i
33、s transmitted together with the speech, would disappear when the transmission is cut, resulting in discontinuities of the background noise. Since the SCR switching can take place rapidly, it has been found that this effect can be very annoying for the listener especially in a car environment with hi
34、gh background noise levels. In bad cases, the speech may be hardly intelligible. This annex specifies the way to overcome this problem by generating on the receive (RX) side synthetic noise similar to the transmit (TX) side background noise. The comfort noise parameters are estimated on the TX side
35、and transmitted to the RX side at a regular rate when speech is not present. This allows the comfort noise to adapt to the changes of the noise on the TX side. A.4 Functions on the transmit (TX) side The comfort noise evaluation algorithm uses the following parameters of the AMR-WB speech encoder, d
36、efined in the main body of ITU-T Rec. G.722.2: the unquantized Linear Prediction (LP) parameters, using the Immittance Spectral Pair (ISP) representation, where the unquantized Immittance Spectral Frequency (ISF) vector is given by f T= f1f2. f16; The algorithm computes the following parameters to a
37、ssist in comfort noise generation: the weighted averaged ISF parameter vector f mean(weighted average of the ISF parameters of the eight most recent frames); ITU-T Rec. G.722.2/Annex A (01/2002) 3 the averaged logarithmic frame energy meanenlog(average of the logarithmic energy of the eight most rec
38、ent frames). These parameters give information on the level (meanenlog) and the spectrum (f mean) of the background noise. The evaluated comfort noise parameters (f meanand meanenlog) are encoded into a special frame, called a Silence Insertion Descriptor (SID) frame, for transmission to the RX side
39、. A hangover logic is used to enhance the quality of the silence descriptor frames. A hangover of seven frames is added to the VAD flag so that the coder waits with the switch from active to inactive mode for a period of seven frames; during that time the decoder can compute a silence descriptor fra
40、me from the quantized ISFs and the logarithmic frame energy of the decoded speech signal. Therefore, no comfort noise description is transmitted in the first SID frame after active speech. If the background noise contains transients which will cause the coder to switch to active mode and then back t
41、o inactive mode in a very short time period, no hangover is used. Instead the previously used comfort noise frames are used for comfort noise generation. The first SID frame also serves to initiate the comfort noise generation on the receive side, as a first SID frame is always sent at the end of a
42、speech burst, i.e. before the transmission is terminated. The scheduling of SID or speech frames on the network path is described in Annex B/G.722.2. A.4.1 ISF evaluation The comfort noise parameters to be encoded into a SID frame are calculated over N = 8 consecutive frames marked with VAD = 0, as
43、follows: Prior to averaging the ISF parameters over the CN averaging period, a median replacement is performed on the set of ISF parameters to be averaged, to remove the parameters which are not characteristic of the background noise on the transmit side. First, the spectral distances from each of t
44、he ISF parameter vectors f(i) to the other ISF parameter vectors f(j), i=0,.,7, j=0,.,7, ij, within the CN averaging period are approximated according to the equation: () ()=1612kjiijkfkfR (A-1) where fi(k) is the kth ISF parameter of the ISF parameter vector f(i) at frame i. To find the spectral di
45、stance Siof the ISF parameter vector f(i) to the ISF parameter vectors f(j) of all the other frames j=0,.,7, ji, within the CN averaging period, the sum of the spectral distances Rijis computed as follows: =7,0 ijjijiRS (A-2) for all i=0,.,7, ij. The ISF parameter vector f(i) with the smallest spect
46、ral distance Siof all the ISF parameter vectors within the CN averaging period is considered as the median ISF parameter vector fmedof the averaging period, and its spectral distance is denoted as Smed. The median ISF parameter vector is considered to contain the best representation of the short-ter
47、m spectral detail of the background noise of all the ISF parameter vectors within the averaging period. If there are ISF parameter vectors f(j) within the CN averaging period with: 4 ITU-T Rec. G.722.2/Annex A (01/2002) medmedjTHSS(A-3) where THmed= 2.25 is the median replacement threshold, then at
48、most two of these ISF parameter vectors (the ISF parameter vectors causing THmedto be exceeded the most) are replaced by the median ISF parameter vector prior to computing the averaged ISF parameter vector f mean. The set of ISF parameter vectors obtained as a result of the median replacement are de
49、noted as f(n i), where n is the index of the current frame, and i is the averaging period index (i=0,.,7). When the median replacement is performed at the end of the hangover period (first CN update), all of the ISF parameter vectors f(n i) of the 7 previous frames (the hangover period, i=1,.,7) have quantized values, while the ISF parameter vector f(n) at the most recent frame n has unquantized values. In the subsequent CN updates, the ISF parameter vectors of the CN averaging period in th
