1、 ETSI TS 1Digital cellular telecoUniversal Mobile TelGeneral audio codEnhanced aaEncoder specif(3GPP TS 26.4TECHNICAL SPECIFICATION126 405 V13.0.0 (2016communications system (Phaelecommunications System (LTE; odec audio processing functiaacPlus general audio codec;cification parametric stereo pa.405
2、 version 13.0.0 Release 1316-01) hase 2+); (UMTS); ctions; c; part 13) ETSI ETSI TS 126 405 V13.0.0 (2016-01)13GPP TS 26.405 version 13.0.0 Release 13Reference RTS/TSGS-0426405vd00 Keywords GSM,LTE,UMTS ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE Tel.: +33 4 92 94 42 00 Fax:
3、+33 4 93 65 47 16 Siret N 348 623 562 00017 - 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 versio
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9、GSM and the GSM logo are Trade Marks registered and owned by the GSM Association. ETSI ETSI TS 126 405 V13.0.0 (2016-01)23GPP TS 26.405 version 13.0.0 Release 13Intellectual Property Rights IPRs essential or potentially essential to the present document 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
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12、tes on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP). The present document may refer to technical specifications or reports using their 3GPP i
13、dentities, UMTS identities or GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables. 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 doc
14、ument “shall“, “shall not“, “should“, “should not“, “may“, “need not“, “will“, “will not“, “can“ and “cannot“ are to be interpreted 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
15、 when used in direct citation. ETSI ETSI TS 126 405 V13.0.0 (2016-01)33GPP TS 26.405 version 13.0.0 Release 13Contents Intellectual Property Rights 2g3Foreword . 2g3Modal verbs terminology 2g3Foreword . 4g31 Scope 5g32 Normative references . 5g33 Definitions, symbols and abbreviations . 5g33.1 Defin
16、itions 5g33.2 Symbols 5g33.3 Abbreviations . 5g34 Outline description . 6g35 Parametric stereo encoder 6g35.1 System overview 6g35.2 Analysis filterbank . 7g35.2.1 QMF analysis filterbank . 7g35.2.2 Low frequency filtering 7g35.3 Configurations 9g35.4 Stereo parameter extraction 9g35.4.1 Parameter e
17、stimation. 9g35.4.2 Quantization of IID and ICC parameters 11g35.5 Writing to bitstream 11g35.6 Downmixing to mono . 13g35.7 Synthesis filterbank 13g3Annex A (informative): Change history . 16g3History 17g3ETSI ETSI TS 126 405 V13.0.0 (2016-01)43GPP TS 26.405 version 13.0.0 Release 13Foreword The pr
18、esent document describes the detailed mapping of the general audio service employing the aacPlus general audio codec 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 cont
19、ents of this TS, it will be re-released by the TSG with an identifying change of release date and an increase in version 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 cont
20、rol. y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates, etc. z the third digit is incremented when editorial only changes have been incorporated in the specification; ETSI ETSI TS 126 405 V13.0.0 (2016-01)53GPP TS 26.405 version 13.0.0
21、Release 131 Scope This Telecommunication Standard (TS) describes the Parametric Stereo encoder part of the Enhanced aacPlus general audio codec 4. 2 Normative references This TS incorporates by dated and undated reference, provisions from other publications. These normative references are cited in t
22、he appropriate places in the text and the publications are listed hereafter. 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
23、referred to applies. 1 ISO/IEC 14496-3:2001/AMD1:2003: “Bandwidth Extension“. 2 ISO/IEC 14496-3:2001/Amd.1:2003/DCOR1. 3 ISO/IEC 14496-3:2001/ Amd.2:2004: “Parametric Coding for High Quality Audio“. 4 3GPP TS 26.401: “Enhanced aacPlus general audio codec; General Description:. 3 Definitions, symbols
24、 and abbreviations 3.1 Definitions For the purposes of this TS, the following definitions apply: hybrid QMF: a QMF filterbank combined with additional filters to achieve higher frequency resolution for the lower QMF bands stereo band: a group of consecutive hybrid QMF subbands used for coding one st
25、ereo parameter 3.2 Symbols For the purposes of this TS, the following symbols apply: Subsample in hybrid QMF matrix: left channel, band k, subsample n. Subsample in hybrid QMF matrix: right channel, band k, subsample n. 3.3 Abbreviations For the purposes of this TS, the following abbreviations apply
26、. SBR Spectral Band Replication AAC Advanced Audio CodingaacPlus Combination of MPEG-4 AAC and MPEG-4 Bandwidth extension (SBR) Enhanced aacPlus Combination of MPEG-4 AAC, MPEG-4 Bandwidth extension (SBR) and MPEG-4 Parametric Stereo QMF Quadrature Mirror Filter MPEG Moving Picture Expert Group IID
27、Inter Intensity Difference, (stereo parameter) ICC Inter Channel Coherence, (stereo parameter) ()kl n()kr nETSI ETSI TS 126 405 V13.0.0 (2016-01)63GPP TS 26.405 version 13.0.0 Release 134 Outline description This TS is structured as follows: Section 5.2 describes the hybrid QMF filterbank and its in
28、tegration in the Parametric Stereo system. Section 5.3 describes the hybrid QMF filterbank and its integration in the Parametric Stereo system. Section 5.4 describes the parameter estimation algorithms and quantization. Section 5.5 describes how to convey the estimated parameters in the bitstream. S
29、ection 5.6 and section 5.7 describes preparation of the signal that should feed the aacPlus mono encoder after the Parametric Stereo encoding. 5 Parametric stereo encoder 5.1 System overview Figure 1: Encoder overview The interface between the parametric stereo encoder tool and the aacPlus encoder i
30、s depicted in Figure 1. In the figure L and R denotes the left and right channel respectively, while M denotes the down-mixed mono signal which the aacPlus encoder operates on. The parametric stereo coding tool is able to capture the stereo image into a limited number of parameters, requiring only a
31、 small overhead of a few kbit/s. Together with a controlled monaural downmix of the stereo input signal, the parametric stereo coding tool is able to regenerate the stereo signal at the decoder side. The encoder operates as a non-modifying analyzer prior to the aacPlus encoder, though it shares the
32、same QMF analysis filterbank. The decoder operates as a post process to aacPlus using the Parametric Stereo data conveyed by the bitstream to synthesize the stereo properties of the output signal. Part from the parametric stereo tool, the aacPlus runs in mono mode not affected by Parametric Stereo.
33、The bitstream syntax and decoder description of the parametric stereo tool in combination with aacPlus is defined in 3. This system includes only the baseline level defined in that standard. QMFanalysis(64 bands)MLHybridsynthesis(to64bands)DownmixtomonoHybridanalysis(77 bands)Stereoparameterextracti
34、onQMF synthesis(32 bands)iid(b),icc(b)PSbitstreamformattingRMAACencoderAACbitstreamSBRbitstreamPSbitstreamSBRencoderLRLRBitstream MUXMETSI ETSI TS 126 405 V13.0.0 (2016-01)73GPP TS 26.405 version 13.0.0 Release 135.2 Analysis filterbank 5.2.1 QMF analysis filterbank This filterbank is identical to t
35、he 64 complex QMF analysis filterbank as defined in ISO/IEC 14496-3/AMD1:2003, sub clause 4.B.18.2 1, 2. However, in the equation for matrix M(k,n) and in Figure 4.B.20, the term (2*n+1) has to be substituted by (2*n-1). The input to the filterbank are blocks of 64 samples of the monaural synthesize
36、d signal M. For each block the filterbank outputs one slot of 64 QMF samples. 5.2.2 Low frequency filtering The lower QMF subbands are further split in order to obtain a higher frequency resolution enabling a proper stereo analysis and synthesis for the lower frequencies. To achieve those, in total
37、77 frequency bands, a hybrid filterbank configurations have been defined. The filter used for this sub subband filtering, is defined according to: where pg represents the prototype filters in QMF subband p. pQ representsthe number of sub-subbands in QMF subband p, q the sub-subband index in QMF chan
38、nel p and n the time index. The prototype filters are all of length 13 and have a delay of 6 QMF samples. The prototype filters are listed in Table 1. Table 1: Prototype filter coefficients for the filters that split the lower QMF subbands 0 0.00746082949812 -0.00305151927305 1 0.02270420949825 -0.0
39、0794862316203 2 0.04546865930473 0 3 0.07266113929591 0.04318924038756 4 0.09885108575264 0.12542448210445 5 0.11793710567217 0.21227807049160 6 0.125 0.25000000000000 7 0.11793710567217 0.21227807049160 8 0.09885108575264 0.12542448210445 9 0.07266113929591 0.04318924038756 10 0.04546865930473 0 11
40、 0.02270420949825 -0.00794862316203 12 0.00746082949812 -0.00305151927305 Figure 2 and Figure 3 illustrate the hybrid analysis and synthesis filterbank for the 77 frequency bands configuration. qpQ() ()21exp 62ppq pGgn j q nQ=+n()00,8gnQ= ()1,2 1,2,4gnQ=ETSI ETSI TS 126 405 V13.0.0 (2016-01)83GPP TS
41、 26.405 version 13.0.0 Release 13Figure 2: Hybrid QMF analysis filterbank providing 77 output bands. The three lower subbands of the 64 QMF (see dashed box) are further split to provide for increased resolution for the lower frequencies )(0H M)(1HM)(63HM)(2HMM()0s n()7sn()8sn()11s n()12s n()15s n()7
42、6s n()07G ()00G ()10G ()13G ()20G ()23G ()630G ETSI ETSI TS 126 405 V13.0.0 (2016-01)93GPP TS 26.405 version 13.0.0 Release 13Figure 3: Hybrid QMF synthesis filterbank using 77 input bands. The coefficients offering higher resolution for the lower QMF subbands are simply added prior to the synthesis
43、 with the 64 subbands QMF (see dashed box) In order to time align all the samples originating from the hybrid filterbank, the remaining QMF subbands that have not been filtered are delay compensated. This delay amounts to 6 QMF subband samples. This means for k=3.63. In order to compensate for the o
44、verall delay of the hybrid analysis filterbank, the first 10 sets (6 from delay and 4 from QMF filter) of hybrid subbands are flushed and therefore not taken into account for processing. The resultant of this operation is a slot of hybrid subband samples consisting of a LF (low frequency) sub QMF su
45、bband portion and HF (high frequency) QMF subband portion. 5.3 Configurations The parametric stereo encoder uses two different configurations depending on desired frequency resolution. The configuration parameter, num_stereo_bands determines what frequency resolution should be used for the stereo pa
46、rameters. For all bitrates below 21000 bit/s, num_stereo_bands is set to 10 otherwise num_stereo_bands is set to 20. 5.4 Stereo parameter extraction 5.4.1 Parameter estimation In order to estimate the stereo parameters the signals M, L and R are analyzed using the hybrid filterbank as in Figure 2 fo
47、r providing the 77 frequency bands addressed by the index, . This results in the (sub-)subband domain signals, , and . To estimate the parameters for the current frame the following is calculated: MM)(0F)(1F)(2F)(63FL,RMM()0,l rn()7,l r n()8,l rn()11,l rn()12,l r n()15,l rn()76,l rn()60kG zz=0 77k=
48、64; n-) vn = vn -64Start( for QMF subsample l )Donefor( n = 0; n 32; n+) vn = in - rnv63-n = in + rnETSI ETSI TS 126 405 V13.0.0 (2016-01)163GPP TS 26.405 version 13.0.0 Release 13Annex A (informative): Change history Change history Date TSG SA# TSG Doc. CR Rev Subject/Comment Old New 2004-09 25 SP-
49、040637 Approved at SA#25 2.0.0 6.0.0 2005-03 27 SP-050095 001 1 Correction to written specification: wrong formula on ICC parameter extraction 6.0.0 6.1.0 2007-06 36 Version for Release 7 6.1.0 7.0.0 2008-12 42 Version for Release 8 7.0.0 8.0.0 2009-12 46 Version for Release 9 8.0.0 9.0.0 2011-03 51 Version for Release 10 9.0.0 10.0.0 2012-09 57 Version for Release 11 10.0.0 11.0.0 2014-09 65 Version for Release 12 11.0.0 12.0.0 2015-12 70 Version for Release 13 12.0.0 13.0.0 ETSI ETSI TS 126 4
