1、 ETSI TS 126 404 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; Enhanced aacPlus encoder Spectral Band Replication (SBR) part
2、(3GPP TS 26.404 version 15.0.0 Release 15) TECHNICAL SPECIFICATION ETSI ETSI TS 126 404 V15.0.0 (2018-07)13GPP TS 26.404 version 15.0.0 Release 15Reference RTS/TSGS-0426404vf00 Keywords GSM,LTE,UMTS ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE Tel.: +33 4 92 94 42 00 Fax: +33
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9、it of its Members. GSMand the GSM logo are trademarks registered and owned by the GSM Association. ETSI ETSI TS 126 404 V15.0.0 (2018-07)23GPP TS 26.404 version 15.0.0 Release 15Intellectual Property Rights Essential patents IPRs essential or potentially essential to normative deliverables may have
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14、rks. 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 identities, UMTS identities or GSM identities. These should be interpreted as being references t
15、o 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 document “shall“, “shall not“, “should“, “should not“, “may“, “need not“, “will“, “will not“, “can
16、“ 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 when used in direct citation. ETSI ETSI TS 126 404 V15.0.0 (2018-07)33GPP TS 26.404 version 15
17、.0.0 Release 15Contents Intellectual Property Rights 2g3Foreword . 2g3Modal verbs terminology 2g3Foreword . 4g31 Scope 5g32 Normative references . 5g33 Definitions, symbols and abbreviations . 5g33.1 Definitions 5g33.2 Symbols 6g33.3 Abbreviations . 7g34 Outline description . 7g35 SBR encoder descri
18、ption 7g35.1 SBR tools overview 7g35.1.1 Enhanced aacPlus sdynchronization without parametric stereo 8g35.1.2 Enhanced aacPlus synchronisation with parametric stereo . 9g35.1.3 SBR encoder modules overview . 10g35.2 Analysis filterbank . 12g35.3 Frequency band tables 15g35.4 Time / frequency grid ge
19、neration . 15g35.4.1 Transient detector . 15g35.4.2 Frame splitter 16g35.4.3 Frame generator 17g35.5 Envelope estimation . 21g35.6 Additional control parameters 22g35.6.1 Introduction. 22g35.6.2 Tonality estimation . 23g35.6.3 Noise-floor estimation 24g35.6.4 Inverse filtering estimation . 25g35.6.5
20、 Additional sines estimation . 26g35.7 Data quantization 29g35.8 Envelope and noise floor coding 30g36 Bitstream 32g3Annex A (informative): Change history . 34g3History 35g3ETSI ETSI TS 126 404 V15.0.0 (2018-07)43GPP TS 26.404 version 15.0.0 Release 15Foreword The present document describes the deta
21、iled 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 contents of this TS, it will be re-re
22、leased 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 control. y the second digit is increm
23、ented 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 126 404 V15.0.0 (2018-07)53GPP TS 26.404 version 15.0.0 Release 151 Scope This Telecommun
24、ication Standard (TS) describes the SBR encoder part of 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 publi
25、cations 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 referred to applies. 1 ISO/IEC 14496-3:2001/Amd
26、.1:2003, Bandwidth Extension. 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
27、floor band, etc.) a group of consecutive QMF subbands chirp factor: the bandwidth expansion factor of the formants described by a LPC polynomial Down Sampled SBR: the SBR Tool with a modified synthesis filterbank resulting in a down sampled output signal with the same sample rate as the input signal
28、 to the SBR Tool. May be used whenever a lower sample rate output is desired. 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 frequenc
29、y border: frequency band delimiter, expressed 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
30、to the envelope adjusted HF generated signal and the energy of the same patch: a number of adjoining QMF subbands moved to a different frequency location SBR envelope: a vector of envelope scalefactors SBR frame: time segment associated with one SBR extension data element SBR range: the frequency ra
31、nge of the signal generated by the SBR algorithm subband: a frequency range represented by one row in a QMF matrix, carrying a 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 gri
32、d: a description of SBR envelope time segments and associated frequency resolution tables as well as description of noise floor time segments ETSI ETSI TS 126 404 V15.0.0 (2018-07)63GPP TS 26.404 version 15.0.0 Release 15time slot: finest resolution in time for SBR envelopes and noise floors. One ti
33、me slot equals two subsamples in the QMF domain 3.2 Symbols For the purposes of this TS, the following symbols apply: Description of variables defined in one sub clause and used in other subclasses. ch is the current channel, and when used as index in vectors left channel is represented by ch= 0 and
34、 right channel is represented ch= 1. EOrighas 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. has two column vectors containing the frequency border table
35、s for low and high frequency resolution. internal sampling frequency of the SBR Tool, twice the sampling frequency of the core coder (after sampling frequency mapping, Table 4.55). The sampling frequency of the SBR enhanced output signal is equal to the internal sampling frequency of the SBR Tool, u
36、nless the SBR Tool is operated in downsampled mode. If the SBR Tool is operated in downsampled mode, the output sampling frequency is equal to the sampling frequency of the core coder. fMasteris of length NMaster+1 and contains QMF master frequency grouping information. fTableHighis of length NHigh+
37、1 and contains frequency borders for high frequency resolution SBR envelopes. fTableLowis of length NLow+1 and contains frequency borders for low frequency resolution SBR envelopes. fTableNoiseis of length NQ+1 and contains frequency borders used by noise floors. kxthe first QMF subband in the SBR r
38、ange. k0the first QMF subband in the fMastertable. LEnumber of SBR envelopes. LQnumber of noise floors. M number of QMF subbands in the SBR range. middleBorder points to a specific time border. NLnumber of limiter bands. NMasternumber of frequency bands in the master frequency resolution table. NQnu
39、mber of noise floor bands. number of frequency bands for low and high frequency resolution. numPatches a variable indicating the number of patches in the SBR range. numTimeSlots number of SBR envelope time slots that exist within an AAC frame, 16 for a 1024 AAC frame . offset-values for the SBR enve
40、lope and noise floor data, when using coupled channels. patchBorders a vector containing the frequency borders of the patches. patchNumSubbands a vector holding the number of subbands in every patch. ,TableLow TableHighg170g186=g172g188Ff fSBRFs, Low HighNN=n24,12=panOffsetETSI ETSI TS 126 404 V15.0
41、.0 (2018-07)73GPP TS 26.404 version 15.0.0 Release 15QOrighas LQcolumns where each column is of length NQand contains the noise floor scalefactors. frequency resolution for all SBR envelopes in the current SBR frame, zero for low resolution, one for high resolution. reset a variable in the encoder a
42、nd the decoder set to one if certain bitstream elements have changed from the previous SBR frame, otherwise set to zero. tEis of length LE+1 and contains start and stop time borders for all SBR envelopes in the current SBR frame. tHFAdjoffset for the envelope adjuster module. tHFGenoffset for the HF
43、-generation module. tQis of length LQ+1 and contains start and stop time borders for all noise floors in the current SBR frame. 3.3 Abbreviations For the purposes of this TS, the following abbreviations apply. NA Not Applicable aacPlus Combination of MPEG-4 AAC and MPEG-4 Bandwidth extension (SBR) E
44、nhanced aacPlus Combination of MPEG-4 AAC, MPEG-4 Bandwidth extension (SBR) and MPEG-4 Parametric Stereo QMF Quadrature Mirror Filter SBR Spectral Band Replication 4 Outline description This TS is structured as follows: Section 5.1 gives an encoder overview description. Section 5.2 gives a detailed
45、description of the filterbanks used in the encoder. Section 5.3 gives a specification of the used frequency band tables. Section 5.4 gives a detailed description of the time grid calculation and the transient detection. Section 5.5 gives a detailed description of the envelope estimation. Section 5.6
46、 gives a detailed description of the estimation of the additional control parameters. Section 5.7 gives detailed description of the data quantisation. Section 5.8 gives a detailed description of the envelope coding. 5 SBR encoder description 5.1 SBR tools overview The encoder part of the SBR tool es
47、timates several parameters used by the high frequency reconstruction method on the decoder side. In order to synchronise the SBR bitstream data with the AAC codec, the two different modes of operation have to be considered; normal aacPlus operation and aacPlus parametric stereo operation. In the nor
48、mal case, the AAC encoder is responsible for downsampling of the input PCM signal, while the SBR encoder works in parallel on twice the sampling frequency compared to the downsampled signal. When using parametric stereo aacPlus, the SBR tool is also responsible for downsampling of the AAC coder sign
49、al. The two modes are outlined in the following sections and illustrated in Figure 1 and Figure 2. 0 1 ,., Lr r=rETSI ETSI TS 126 404 V15.0.0 (2018-07)83GPP TS 26.404 version 15.0.0 Release 15Figure 1 aacPlus block diagram Figure 2 Parametric stereo aacPlus block diagram 5.1.1 Enhanced aacPlus sdynchronization without parametric stereo The time domain input PCM signal is assumed to be stored in a buffer x, where 2048 new samples are added to the end of the buffer every frame. Before adding new samples, all samples in the buffer must be left-shifted 2048 samples.
