1、 ETSI TS 126 405 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; Encoder specification parametric stereo part (3GPP TS 26.405 v
2、ersion 15.0.0 Release 15) TECHNICAL SPECIFICATION ETSI ETSI TS 126 405 V15.0.0 (2018-07)13GPP TS 26.405 version 15.0.0 Release 15Reference RTS/TSGS-0426405vf00 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 Sir
3、et 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 versions and/or in print. T
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9、. GSMand the GSM logo are trademarks registered and owned by the GSM Association. ETSI ETSI TS 126 405 V15.0.0 (2018-07)23GPP TS 26.405 version 15.0.0 Release 15Intellectual Property Rights Essential patents IPRs essential or potentially essential to normative deliverables may have been declared to
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13、h are indicated as being 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 Thi
14、s 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 identities, UMTS identities or GSM identities. These should be interpreted as being references to the correspondi
15、ng 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 document “shall“, “shall not“, “should“, “should not“, “may“, “need not“, “will“, “will not“, “can“ and “cannot“ ar
16、e 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 when used in direct citation. ETSI ETSI TS 126 405 V15.0.0 (2018-07)33GPP TS 26.405 version 15.0.0 Release 15Co
17、ntents Intellectual 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 . 5g34 Outline description . 5g35 Parametric stereo encoder 6g35.1 Sy
18、stem overview 6g35.2 Analysis filterbank . 6g35.2.1 QMF analysis filterbank . 6g35.2.2 Low frequency filtering 7g35.3 Configurations 9g35.4 Stereo parameter extraction 9g35.4.1 Parameter estimation. 9g35.4.2 Quantization of IID and ICC parameters 11g35.5 Writing to bitstream 11g35.6 Downmixing to mo
19、no . 12g35.7 Synthesis filterbank 13g3Annex A (informative): Change history . 15g3History 16g3ETSI ETSI TS 126 405 V15.0.0 (2018-07)43GPP TS 26.405 version 15.0.0 Release 15Foreword The present document describes the detailed mapping of the general audio service employing the aacPlus general audio c
20、odec 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
21、 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 control. y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, u
22、pdates, etc. z the third digit is incremented when editorial only changes have been incorporated in the specification; ETSI ETSI TS 126 405 V15.0.0 (2018-07)53GPP TS 26.405 version 15.0.0 Release 151 Scope This Telecommunication Standard (TS) describes the Parametric Stereo encoder part of the Enhan
23、ced 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 the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent am
24、endments 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/AMD1:2003: “Bandwidth Extension“. 2 ISO/IEC 14496-3:2001/Amd.1:2003/
25、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 and abbreviations 3.1 Definitions For the purposes of this TS, the following definitions apply: hybrid QMF: a Q
26、MF 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 stereo parameter 3.2 Symbols For the purposes of this TS, the following symbols apply: Subsample in hybrid QMF mat
27、rix: 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. SBR Spectral Band Replication AAC Advanced Audio CodingaacPlus Combination of MPEG-4 AAC and MPEG-4 Bandwidth
28、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 Inter Intensity Difference, (stereo parameter) ICC Inter Channel Coherence, (stereo parameter) 4 Outline descrip
29、tion This TS is structured as follows: ()kl n()kr nETSI ETSI TS 126 405 V15.0.0 (2018-07)63GPP TS 26.405 version 15.0.0 Release 15Section 5.2 describes the hybrid QMF filterbank and its integration in the Parametric Stereo system. Section 5.3 describes the hybrid QMF filterbank and its integration i
30、n 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. Section 5.6 and section 5.7 describes preparation of the signal that should feed the aacPlus mono encoder after t
31、he 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 is depicted in Figure 1. In the figure L and R denotes the left and right channel respectively, while M denotes t
32、he 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 small overhead of a few kbit/s. Together with a controlled monaural downmix of the stereo input signal, the par
33、ametric 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 same QMF analysis filterbank. The decoder operates as a post process to aacPlus using the Parametric Stereo data
34、 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. The bitstream syntax and decoder description of the parametric stereo tool in combination with aacPlus is define
35、d in 3. This system includes only the baseline level defined in that standard. 5.2 Analysis filterbank 5.2.1 QMF analysis filterbank This filterbank is identical to the 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
36、matrix M(k,n) and in Figure 4.B.20, the term “(2*n+1)“ has to be QMFanalysis(64bands)MLHybridsynthesis(to 64bands)DownmixtomonoHybrid analysis(77bands)StereoparameterextractionQMFsynthesis(32 bands)iid(b),icc(b)PSbitstreamformattingRMAACencoderAACbitstreamSBRbitstreamPSbitstreamSBRencoderLRLRBitstre
37、amMUXMETSI ETSI TS 126 405 V15.0.0 (2018-07)73GPP TS 26.405 version 15.0.0 Release 15substituted by “(2*n-1)“. The input to the filterbank are blocks of 64 samples of the monaural synthesized signal M. For each block the filterbank outputs one slot of 64 QMF samples. 5.2.2 Low frequency filtering Th
38、e 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 77 frequency bands, a hybrid filterbank configurations have been defined. The filter used for this sub subband
39、 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 channel p and n the time index. The prototype filters are all of length 13 and have a delay of 6 QMF samples. The
40、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 -0.00794862316203 2 0.04546865930473 0 3 0.07266113929591 0.04318924038756 4 0.09885108575264 0.12542448210445 5 0
41、.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 0.02270420949825 -0.00794862316203 12 0.00746082949812 -0.00305151927305 Figure 2 and Figure 3 illustrate the
42、 hybrid analysis and synthesis filterbank for the 77 frequency bands configuration. qpQ() ()21exp 62ppq pGgn j q nQg167g183g167g183=+g168g184g168g184g169g185g169g185n()00,8gnQ= ()1,2 1,2,4gnQ=ETSI ETSI TS 126 405 V15.0.0 (2018-07)83GPP TS 26.405 version 15.0.0 Release 15Figure 2: Hybrid QMF analysis
43、 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()76s n()07G ()00G ()10G ()13G ()20G ()23G ()630G ETSI ETSI TS 12
44、6 405 V15.0.0 (2018-07)93GPP TS 26.405 version 15.0.0 Release 15Figure 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 with the 64 subbands QMF (see dashed box) In order to time al
45、ign 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 overall delay of the hybrid analysis filterbank, the first 10 s
46、ets (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 subband portion and HF (high frequency) QMF subband portion. 5.3
47、 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 parameters. For all bitrates below 21000 bit/s, num_stereo_bands
48、 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 for providing the 77 frequency bands addressed by the index, . T
49、his 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= 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 V15.0.0 (2018-07)153GPP TS 26.405 version 15.0.0 Release 15Annex A (informative): Change history Change history Date TSG SA# TSG Doc. CR Rev Subject/Comment Old New
