1、 ETSI TS 1Digital cellular telecoUniversal Mobile TelGeneral audio codEnhanced aaAddit(3GPP TS 26.4TECHNICAL SPECIFICATION126 402 V13.0.0 (2016communications system (Phaelecommunications System (LTE; odec audio processing functiaacPlus general audio codec;ditional decoder tools .402 version 13.0.0 R
2、elease 1316-01) hase 2+); (UMTS); ctions; c; 13) ETSI ETSI TS 126 402 V13.0.0 (2016-01)13GPP TS 26.402 version 13.0.0 Release 13Reference RTS/TSGS-0426402vd00 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 Sire
3、t 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. Th
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9、re Trade Marks registered and owned by the GSM Association. ETSI ETSI TS 126 402 V13.0.0 (2016-01)23GPP TS 26.402 version 13.0.0 Release 13Intellectual Property Rights IPRs essential or potentially essential to the present document may have been declared to ETSI. The information pertaining to these
10、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 Secretariat. Latest up
11、dates 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 updates on the ETSI Web se
12、rver) 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 identities, UMTS identi
13、ties 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 document “shall“, “shall
14、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 when used in direct c
15、itation. ETSI ETSI TS 126 402 V13.0.0 (2016-01)33GPP TS 26.402 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 Definitions 5g33.2 Symbols
16、6g33.3 Abbreviations . 6g34 Outline description . 7g35 Error concealment 7g35.1 AAC error concealment 7g35.2 SBR error concealment 8g36 SBR stereo parameter to mono parameter downmix 11g36.1 Inverse filtering 11g36.2 Additional harmonics . 11g36.3 Envelope time borders 12g36.4 Noise time borders 12g
17、36.5 Envelope data . 13g36.6 Noise floor data 14g37 Output resampler tool . 14g37.1 QMF bandlimiter 14g37.2 Spline resampler . 15g37.3 Postfilter . 15g3Annex A (informative): Change history . 17g3History 18g3ETSI ETSI TS 126 402 V13.0.0 (2016-01)43GPP TS 26.402 version 13.0.0 Release 13Foreword The
18、present document describes tools used in the Enhanced aacPlus general audio codec for the general audio service 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
19、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 control.
20、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 126 402 V13.0.0 (2016-01)53GPP TS 26.402 version 13.0.0 Relea
21、se 131 Scope This Telecommunication Standard (TS) describes the error concealment algorithm, SBR parameter downmix 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. The
22、se normative references are cited in the 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,
23、the latest edition of the publication referred to applies. 1 ISO/IEC 14496-3:2001/Amd.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 th
24、e purposes of this TS, the following definitions apply: band: (as in limiter band, noise floor band, etc.) a group 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:
25、interval in frequency, group of consecutive QMF subbands frequency 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, re
26、presenting the ratio between the energy of the noise to be added to the envelope adjusted HF generated signal 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
27、 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 grid: a description
28、of SBR envelope time segments and associated frequency resolution tables as well as description of noise floor time segments time slot: finest resolution in time for SBR envelopes and noise floors. One time slot equals two subsamples in the QMF domain ETSI ETSI TS 126 402 V13.0.0 (2016-01)63GPP TS 2
29、6.402 version 13.0.0 Release 133.2 Symbols For the purposes of this TS, the following symbols apply: 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 sign
30、al. the output sampling rate from the SBR Tool. internal sampling frequency of the SBR Tool, twice the sampling 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
31、 frequency of the SBR Tool, unless 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. has two column vectors containing the frequency border tables for low and high frequen
32、cy resolution. fTableHighis of length NHigh+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. LEnumber of SBR envelopes. LQnumber of noise floors. NQnumber of noise flo
33、or bands. number of frequency bands for low and high frequency resolution. numTimeSlots number of SBR envelope 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
34、 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. tEis of length LE+1 and contains start and stop time borders for all SBR envelopes in the curr
35、ent SBR frame. tQis of length LQ+1 and contains start and stop time borders for all noise floors in the current 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
36、 aacPlus 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 MPEG Moving Picture Experts Group SBR Spectral Band Replication outFsSBRFsoutFs,TableLow TableHigh=Ff f, Low HighNN=n24,12
37、=panOffset0 1 ,., Lr r=rETSI ETSI TS 126 402 V13.0.0 (2016-01)73GPP TS 26.402 version 13.0.0 Release 134 Outline description This TS is structured as follows: Section 5 gives a detailed description of the error concealment algorithms in the Enhanced aacPlus decoder. In Section 5.1 the error concealm
38、ent of the AAC is described, and in section 5.2 the error concealment of the SBR algorithm is 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 E
39、nhanced aacPlus codec to give output sampling rates of 8 and 16kHz, disregarded the sampling rate 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 test
40、s inside the core decoder, starting with simple CRC tests and ending in a variety of plausibility 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 frame
41、OK flag. This is used for error detection on the transport layer. Concealment works on the spectral 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 th
42、e missing frame. Always the previous frame will be processed by the frequency to time conversion, 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, c
43、oncealment implements first a fade out based on slightly modified spectral values from the last 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
44、be interpolated is the frame n-1 and the last but one frame has the number n-2. The determination of window sequence and the window shape of the corrupt frame follows from the table below: ETSI ETSI TS 126 402 V13.0.0 (2016-01)83GPP TS 26.402 version 13.0.0 Release 13Table 1: Interpolated window seq
45、uences 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_SEQUENCE or LONG_START_SEQUENCE or LONG_STOP_SEQUENCE ONLY_LONG_SEQUENCE 0 ONLY_LONG_SEQUENCE or LONG_START_SEQUENCE or LONG_S
46、TOP_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_START_SEQUENCE or LONG_STOP_SEQUENCE LONG_STOP_SEQUENCE 0 The scalefactor band energies of frames n-2 and n are calculated. If the
47、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 energies are calculated for long block scalefactor bands by mapping the frequency line index of short block spectral coefficients t
48、o 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
49、 the actual frame n is modified by the interpolation factor. This factor is constant over the range of each scalefactor band and is derived from the scalefactor band energy differences of frames n-2 and n. Finally the sign of the interpolated spectral coefficients will be flipped randomly. Fade out and in: A complete fading out takes 5 frames. The spectral coefficients from the last good frame are copied and attenuated by a factor of: with as frame counter since the last good frame. After 5 frames of fading out the concealment switches to muting, that means
