1、 ETSI TS 126 402 V15.0.0 (2018-07) Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); LTE; General audio codec audio processing functions; Enhanced aacPlus general audio codec; Additional decoder tools (3GPP TS 26.402 version 15.0.0 Releas
2、e 15) TECHNICAL SPECIFICATION ETSI ETSI TS 126 402 V15.0.0 (2018-07)13GPP TS 26.402 version 15.0.0 Release 15Reference RTS/TSGS-0426402vf00 Keywords GSM,LTE,UMTS ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE Tel.: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16 Siret N 348 623 562 000
3、17 - NAF 742 C Association but non lucratif enregistre la Sous-Prfecture de Grasse (06) N 7803/88 Important notice The present document can be downloaded from: http:/www.etsi.org/standards-search The present document may be made available in electronic versions and/or in print. The content of any el
4、ectronic and/or print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any existing or perceived difference in contents between such versions and/or in print, the only prevailing document is the print of the Portable Document Format (
5、PDF) version kept on a specific network drive within ETSI Secretariat. Users of the present document should be aware that the document may be subject to revision or change of status. Information on the current status of this and other ETSI documents is available at https:/portal.etsi.org/TB/ETSIDeli
6、verableStatus.aspx If you find errors in the present document, please send your comment to one of the following services: https:/portal.etsi.org/People/CommiteeSupportStaff.aspx Copyright Notification No part may be reproduced or utilized in any form or by any means, electronic or mechanical, includ
7、ing photocopying and microfilm except as authorized by written permission of ETSI. The content of the PDF version shall not be modified without the written authorization of ETSI. The copyright and the foregoing restriction extend to reproduction in all media. ETSI 2018. All rights reserved. DECTTM,
8、PLUGTESTSTM, UMTSTMand the ETSI logo are trademarks of ETSI registered for the benefit of its Members. 3GPPTM and LTETMare trademarks of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners. oneM2M logo is protected for the benefit of its Members. GSMand the GSM log
9、o are trademarks registered and owned by the GSM Association. ETSI ETSI TS 126 402 V15.0.0 (2018-07)23GPP TS 26.402 version 15.0.0 Release 15Intellectual Property Rights Essential patents IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The informatio
10、n pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found in ETSI SR 000 314: “Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect of ETSI standards“, which is available from the ETSI
11、Secretariat. Latest updates are available on the ETSI Web server (https:/ipr.etsi.org/). Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the upda
12、tes on the ETSI Web server) which are, or may be, or may become, essential to the present document. Trademarks The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners. ETSI claims no ownership of these except for any which are indicated as b
13、eing the property of ETSI, and conveys no right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks. Foreword This Technical Specific
14、ation (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP). The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables
15、. The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under http:/webapp.etsi.org/key/queryform.asp. Modal verbs terminology In the present document “shall“, “shall not“, “should“, “should not“, “may“, “need not“, “will“, “will not“, “can“ and “cannot“ are to be interpreted
16、as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions). “must“ and “must not“ are NOT allowed in ETSI deliverables except when used in direct citation. ETSI ETSI TS 126 402 V15.0.0 (2018-07)33GPP TS 26.402 version 15.0.0 Release 15Contents Intellectual
17、Property Rights 2g3Foreword . 2g3Modal verbs terminology 2g3Foreword . 4g31 Scope 5g32 Normative references . 5g33 Definitions, symbols and abbreviations . 5g33.1 Definitions 5g33.2 Symbols 5g33.3 Abbreviations . 6g34 Outline description . 6g35 Error concealment 7g35.1 AAC error concealment 7g35.2 S
18、BR error concealment 8g36 SBR stereo parameter to mono parameter downmix 10g36.1 Inverse filtering 10g36.2 Additional harmonics . 11g36.3 Envelope time borders 11g36.4 Noise time borders 11g36.5 Envelope data . 12g36.6 Noise floor data 13g37 Output resampler tool . 13g37.1 QMF bandlimiter 13g37.2 Sp
19、line resampler . 14g37.3 Postfilter . 14g3Annex A (informative): Change history . 16g3History 17g3ETSI ETSI TS 126 402 V15.0.0 (2018-07)43GPP TS 26.402 version 15.0.0 Release 15Foreword The present document describes tools used in the Enhanced aacPlus general audio codec for the general audio servic
20、e within the 3GPP system. The contents of the present document are subject to continuing work within the TSG and may change following formal TSG approval. Should the TSG modify the contents of this TS, it will be re-released by the TSG with an identifying change of release date and an increase in ve
21、rsion number as follows: Version x.y.z where: x the first digit: 1 presented to TSG for information; 2 presented to TSG for approval; 3 Indicates TSG approved document under change control. y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, upda
22、tes, etc. z the third digit is incremented when editorial only changes have been incorporated in the specification; ETSI ETSI TS 126 402 V15.0.0 (2018-07)53GPP TS 26.402 version 15.0.0 Release 151 Scope This Telecommunication Standard (TS) describes the error concealment algorithm, SBR parameter dow
23、nmix and output resampling for the Enhanced aacPlus general audio codec 3. 2 Normative references This TS incorporates by dated and undated reference, provisions from other publications. These normative references are cited in the appropriate places in the text and the publications are listed hereaf
24、ter. For dated references, subsequent amendments to or revisions of any of these publications apply to this TS only when incorporated in it by amendment or revision. For undated references, the latest edition of the publication referred to applies. 1 ISO/IEC 14496-3:2001/Amd.1:2003: “Bandwidth Exten
25、sion“. 2 ISO/IEC 14496-3:2001/Amd.1:2003/DCOR1. 3 3GPP TS 26.401: “Enhanced aacPlus general audio codec; General Description“. 3 Definitions, symbols and abbreviations 3.1 Definitions For the purposes of this TS, the following definitions apply: band: (as in limiter band, noise floor band, etc.) a g
26、roup of consecutive QMF subbands envelope scalefactor: an element representing the averaged energy of a signal over a region described by a frequency band and a time segment frequency band: interval in frequency, group of consecutive QMF subbands frequency border: frequency band delimiter, expressed
27、 as a specific QMF subband noise floor: a vector of noise floor scalefactors noise floor scalefactor: an element associated with a region described by a frequency band and a time segment, representing the ratio between the energy of the noise to be added to the envelope adjusted HF generated signal
28、and the energy of the same SBR envelope: a vector of envelope scalefactors SBR frame: time segment associated with one SBR extension data element SBR range: the frequency range of the signal generated by the SBR algorithm subband: a frequency range represented by one row in a QMF matrix, carrying a
29、subsampled signal time border: time segment delimiter, expressed as a specific time slot time segment: interval in time, group of consecutive time slots time / frequency grid: a description of SBR envelope time segments and associated frequency resolution tables as well as description of noise floor
30、 time segments time slot: finest resolution in time for SBR envelopes and noise floors. One time slot equals two subsamples in the QMF domain 3.2 Symbols For the purposes of this TS, the following symbols apply: ETSI ETSI TS 126 402 V15.0.0 (2018-07)63GPP TS 26.402 version 15.0.0 Release 15EOrighas
31、LEcolumns where each column is of length NLowor NHighdepending on the frequency resolution for each SBR envelope. The elements in EOrigcontains the envelope scalefactors of the original signal. the output sampling rate from the SBR Tool. internal sampling frequency of the SBR Tool, twice the samplin
32、g frequency of the core coder (after sampling frequency mapping, ISO/IEC 14496-3:2001, Table 4.55). The sampling frequency of the SBR enhanced output signal is equal to the internal sampling frequency of the SBR Tool, unless the SBR Tool is operated in downsampled mode. If the SBR Tool is operated i
33、n downsampled mode, the output sampling frequency is equal to the sampling frequency of the core coder. has two column vectors containing the frequency border tables for low and high frequency resolution. fTableHighis of length NHigh+1 and contains frequency borders for high frequency resolution SBR
34、 envelopes. fTableLowis of length NLow+1 and contains frequency borders for low frequency resolution SBR envelopes. LEnumber of SBR envelopes. LQnumber of noise floors. NQnumber of noise floor bands. number of frequency bands for low and high frequency resolution. numTimeSlots number of SBR envelope
35、 time slots that exist within an AAC frame, 16 for a 1024 AAC frame and 15 for a 960 AAC frame. offset-values for the SBR envelope and noise floor data, when using coupled channels. QOrighas LQcolumns where each column is of length NQand contains the noise floor scalefactors. frequency resolution fo
36、r all SBR envelopes in the current SBR frame, zero for low resolution, one for high resolution. tEis of length LE+1 and contains start and stop time borders for all SBR envelopes in the current SBR frame. tQis of length LQ+1 and contains start and stop time borders for all noise floors in the curren
37、t SBR frame. Y is the complex output QMF bank subband matrix from the HF adjuster. 3.3 Abbreviations For the purposes of this TS, the following abbreviations apply. AAC Advanced Audio Coding aacPlus Combination of MPEG-4 AAC and MPEG-4 Bandwidth extension (SBR) Enhanced aacPlus Combination of MPEG-4
38、 AAC, MPEG-4 Bandwidth extension (SBR) and MPEG-4 Parametric Stereo MPEG Moving Picture Experts Group SBR Spectral Band Replication 4 Outline description This TS is structured as follows: outFsSBRFsoutFs,TableLow TableHighg170g186=g172g188Ff f, Low HighNN=n24,12=panOffset0 1 ,., Lr r=rETSI ETSI TS 1
39、26 402 V15.0.0 (2018-07)73GPP TS 26.402 version 15.0.0 Release 15Section 5 gives a detailed description of the error concealment algorithms in the Enhanced aacPlus decoder. In Section 5.1 the error concealment of the AAC is described, and in section 5.2 the error concealment of the SBR algorithm is
40、outlined. Section 6 gives a detailed description of how stereo SBR parameters are down mixed to mono SBR parameters. Section 7 gives a detailed description of the additional downsampler tool, enabling the Enhanced aacPlus codec to give output sampling rates of 8 and 16kHz, disregarded the sampling r
41、ate used for the coded signal. 5 Error concealment 5.1 AAC error concealment The AAC core decoder includes a concealment function that increases the delay of the decoder by one frame. There are various tests inside the core decoder, starting with simple CRC tests and ending in a variety of plausibil
42、ity checks. If such a check indicates an invalid bitstream, then concealment is applied. Concealment is also applied when the calling main program indicates a distorted or missing data frame using the frameOK flag. This is used for error detection on the transport layer. Concealment works on the spe
43、ctral data just before the final frequency to time conversion. In case a single frame is corrupted, concealment interpolates between the last good and the first good frame to create the spectral data for the missing frame. Always the previous frame will be processed by the frequency to time conversi
44、on, so here the missing frame to be replaced is the previous frame, the last good frame is the frame before the previous one and the first good frame is the actual frame. If multiple frames are corrupted, concealment implements first a fade out based on slightly modified spectral values from the las
45、t good frame. As soon as good frames are available, concealment fades in the new spectral data. Interpolation of one corrupt frame: In the following the actual frame is frame number n, the corrupt frame to be interpolated is the frame n-1 and the last but one frame has the number n-2. The determinat
46、ion of window sequence and the window shape of the corrupt frame follows from the table below: Table 1: Interpolated window sequences and window shapes window sequence n-2 window sequence n window sequence n-1 window shape n-1 ONLY_LONG_SEQUENCE or LONG_START_SEQUENCE or LONG_STOP_SEQUENCE ONLY_LONG
47、_SEQUENCE or LONG_START_SEQUENCE or LONG_STOP_SEQUENCE ONLY_LONG_SEQUENCE 0 ONLY_LONG_SEQUENCE or LONG_START_SEQUENCE or LONG_STOP_SEQUENCE EIGHT_SHORT_SEQUENCE LONG_START_SEQUENCE 1 EIGHT_SHORT_SEQUENCE EIGHT_SHORT_SEQUENCE EIGHT_SHORT_SEQUENCE 1 EIGHT_SHORT SEQUENCE ONLY_LONG_SEQUENCE or LONG_STAR
48、T_SEQUENCE or LONG_STOP_SEQUENCE LONG_STOP_SEQUENCE 0 The scalefactor band energies of frames n-2 and n are calculated. If the window sequence in one of these frames is an EIGHT_SHORT_SEQUENCE and the final window sequence for frame n-1 is one of the long transform windows, the scalefactor band ener
49、gies are calculated for long block scalefactor bands by mapping the frequency line index of short ETSI ETSI TS 126 402 V15.0.0 (2018-07)83GPP TS 26.402 version 15.0.0 Release 15block spectral coefficients to a long block representation. The new interpolated spectrum is built by reusing the spectrum of the older frame n-2 multiplying a factor to each spectral coefficient. An exception is made in the case of a short window sequence in frame n-2 and a long window sequence in frame n, here the spectrum of the actual frame n is modified by the interpolation factor. T
