1、 ETSI TS 126 401 V14.0.0 (2017-04) Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); LTE; General audio codec audio processing functions; Enhanced aacPlus general audio codec; General description (3GPP TS 26.401 version 14.0.0 Release 14)
2、 TECHNICAL SPECIFICATION ETSI ETSI TS 126 401 V14.0.0 (2017-04)13GPP TS 26.401 version 14.0.0 Release 14Reference RTS/TSGS-0426401ve00 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 00017 -
3、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 electro
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8、te 2017. All rights reserved. DECTTM, PLUGTESTSTM, UMTSTMand the ETSI logo are Trade Marks of ETSI registered for the benefit of its Members. 3GPPTM and LTE are Trade Marks of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners. GSM and the GSM logo are Trade Marks
9、 registered and owned by the GSM Association. ETSI ETSI TS 126 401 V14.0.0 (2017-04)23GPP TS 26.401 version 14.0.0 Release 14Intellectual Property Rights IPRs essential or potentially essential to the present document may have been declared to ETSI. The information pertaining to these essential IPRs
10、, 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 updates are avai
11、lable 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 server) which ar
12、e, 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 identities or GSM id
13、entities. 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 not“, “should“
14、, “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 citation. ETSI
15、ETSI TS 126 401 V14.0.0 (2017-04)33GPP TS 26.401 version 14.0.0 Release 14Contents Intellectual Property Rights 2g3Foreword . 2g3Modal verbs terminology 2g3Foreword . 4g31 Scope 5g32 Normative references . 5g33 Abbreviations . 5g34 Outline description . 6g35 General . 6g36 Enhanced aacPlus general a
16、udio codec: ANSI-C code 7g37 Enhanced aacPlus general audio codec: Enhanced aacPlus encoder . 7g38 Enhanced aacPlus general audio codec: Enhanced aacPlus decoder . 8g39 Enhanced aacPlus general audio codec: Additional Decoder Tools 9g310 Enhanced aacPlus general audio codec: Compatibility 10g311 SBR
17、 Signalling in Payload formats 10g3Annex A (informative): Change history . 12g3History 13g3ETSI ETSI TS 126 401 V14.0.0 (2017-04)43GPP TS 26.401 version 14.0.0 Release 14Foreword The present document describes the Enhanced aacPlus general audio codec within the 3GPP system. The contents of the prese
18、nt 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 version number as follows: Version x.y.z where: x the
19、 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, updates, etc. z the third digit is incremented when edi
20、torial only changes have been incorporated in the specification; ETSI ETSI TS 126 401 V14.0.0 (2017-04)53GPP TS 26.401 version 14.0.0 Release 141 Scope This Telecommunication Standard (TS) describes the detailed mapping from an MPEG-4 bitstream containing Enhanced aacPlus coded audio to PCM sample o
21、utput. The Enhanced aacPlus audio codec is based on the AAC, SBR and Parametric Stereo coding tools defined in the MPEG-4 Audio standard 567. In addition it includes further tools such as error concealment, spline resampler, and stereo-to-mono downmix. This Telecommunication Standard (TS) also descr
22、ibes the detailed mapping from a PCM sample input to an MPEG-4 bitstream containing Enhanced aacPlus coded audio. 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
23、 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 referred to applies. 1 3GPP TS 26
24、.410 : Enhanced aacPlus general audio codec; Floating-point ANSI-C Code. 2 3GPP TS 26.403 : Enhanced aacPlus general audio codec; Encoder Specification AAC part. 3 3GPP TS 26.404 : Enhanced aacPlus general audio codec; Encoder Specification SBR part. 4 3GPP TS 26.405 : Enhanced aacPlus general audio
25、 codec; Encoder Specification Parametric Stereo part. 5 ISO/IEC 14496-3:2001, Information technology - Coding of audio-visual objects - Part 3: Audio. 6 ISO/IEC 14496-3:2001/Amd.1:2003, Bandwidth Extension. 7 ISO/IEC 14496-3:2001/Amd.1:2003/DCOR1. 8 ISO/IEC 14496-3:2001/Amd.2:2004, Parametric Coding
26、 for High Quality Audio. 9 3GPP TS 26.402: Enhanced aacPlus general audio codec; Additional Decoder Tools. 10 3GPP TS 26.411 : Enhanced aacPlus general audio codec; Fixed-point ANSI-C Code. 11 3GPP TS 26.234 : Transparent end-to-end Packet-switched Streaming Service (PSS) ; Protocols and codecs. 12
27、ISO/IEC 14496-3:2001/Amd.2:2004/DCOR 1. 3 Abbreviations For the purposes of this TS, the following abbreviations apply. AAC Advanced Audio Coding AAC-LC Advanced Audio Coding Low Complexity Object Type AAC-LTP Advanced Audio Coding Long Term Predictor Object Type aacPlus MPEG-4 High Efficiency AAC,
28、the combination of MPEG-4 AAC and MPEG-4 Bandwidth extension (SBR) Enhanced aacPlus MPEG-4 High Efficiency AAC plus MPEG-4 Parametric StereoMDCT Modified Discrete Cosine Transform QMF Quadrature Mirror Filter SBR Spectral Band Replication ETSI ETSI TS 126 401 V14.0.0 (2017-04)63GPP TS 26.401 version
29、 14.0.0 Release 144 Outline description This TS is structured as follows: Section 5 gives a general overview of the parts in the Enhanced aacPlus codec. It further specifies what parts of the cited ISO standards apply. Section 7 gives a more detailed overview of the Enhanced aacPlus encoder, and ref
30、erences the relevant detailed technical description documents. Section 8 gives a more detailed overview of the ISO standardised parts of the Enhanced aacPlus decoder, and references the relevant ISO standards. Section 9 gives a more detailed overview of the additional tools present in the Enhanced a
31、acPlus decoder that are not part of the cited ISO standards, and references the relevant detailed technical description documents. 5 General The Enhanced aacPlus general audio codec consists of MPEG-4 AAC, MPEG-4 SBR and MPEG-4 Parametric Stereo. The AAC is a general audio codec, SBR is a bandwidth
32、extension technique offering substantial coding gain in combination with AAC, and Parametric Stereo enables stereo coding at very low bitrates. In addition to the above parts of the Enhanced aacPlus codec that are specified in ISO standards 567812 there are 3 additional tools included in the Enhance
33、d aacPlus decoder: - Error concealment tools for AAC, SBR, and Parametric Stereo make the decoder robust against transmission errors like frame loss. These tools mitigate audible effects of such errors. - The stereo-to-mono downmix tool enables a decoder only capable of mono output to downmix a ster
34、eo bitstream. For the AAC part this is done in the time domain after the stereo decoding but for SBR this is done on the SBR parameters and thus saving complexity since only a mono decoding of SBR is needed. - The Spline resampler tool gives the possibility to resample the output to a sampling frequ
35、ency different than what was supplied in the bitstream. This gives for example handsets with a D/A converter only capable of 16 kHz sampling frequency the possibility to play bit streams encoded with 22.05 kHz sampling frequency. The 3GPP Enhanced aacPlus general audio codec offers monophonic and st
36、ereophonic coding. For stereophonic coding two stereo modes are used: parametric stereo for low bitrates and M/S stereo for high bitrates. The codec is based on the MPEG-4 Audio ISO standard. The cited ISO standards define several profiles and levels of which not all are applicable in the 3GPP conte
37、xt. From the ISO standards the following subset shall be used: The Enhanced aacPlus general audio codec implements the High Efficiency AAC Profile at Level 21as defined in 6. In addition, the following restriction applies: - frameLengthFlag in GASpecificConfig() shall be 0 (i.e., 960 framing is not
38、supported); For terminals supporting stereophonic output the following additional statements apply: - for mono and parametric stereo bitstreams, the Enhanced aacPlus decoder operates the SBR tool in HQ mode, thus the SBR HQ tool is required; - the parametric stereo enhancement implements the baselin
39、e version of the parametric stereo coding tool in direct combination with the SBR tool, as defined in 8. - for M/S stereo bitstreams, it is recommended that the Enhanced aacPlus decoder operates the SBR tool in Low Power mode. 1The HE-AAC Profile combines the AAC Low Complexity object type plus the
40、SBR tool. The AAC LC object type does not implement the Long Term Predictor (LTP) tool. The Level 2 implies a restriction to a maximum of two channels. Furthermore in case of SBR being used, the maximum AAC sampling rate is restricted to 24 kHz whereas if SBR is not used the maximum AAC sampling rat
41、e is restricted to 48 kHz. ETSI ETSI TS 126 401 V14.0.0 (2017-04)73GPP TS 26.401 version 14.0.0 Release 14For terminals that are only capable of producing monophonic output the following additional statements apply: - implementation of the parametric stereo tool is not required. The decoder would sk
42、ip the parametric stereo data and only decode the mono portion of the signal. - the stereo-to-mono-downmix tool is required in order to be able to decode M/S stereo bitstreams. - implementation of the SBR HQ tool is not required. Instead it is recommended to only implement the SBR Low Power tool sin
43、ce it allows for reduced computational complexity and lower memory requirements Figure 1 illustrates how the AAC, SBR and the Parametric Stereo tools are combined to form the enhanced aacPlus codec: aacPlus consists of AAC and SBR. Enhanced aacPlus consists of aacPlus and the additional Parametric S
44、tereo tool. Enhanced aacPlus is thus a true superset of aacPlus and AAC. aacPlus(= MPEG-4 High Efficiency AAC)Enhanced aacPlus(= MPEG-4 High Efficiency AAC + MPEG-4 Parametric Stereo)AAC-LC SBRParametricStereoFigure 1: MPEG tools used to form the Enhanced aacPlus codec 6 Enhanced aacPlus general aud
45、io codec: ANSI-C code The Floating-point ANSI C-code of the general audio codec Enhanced aacPlus is described in 1. The Fixed-point ANSI C-code of the general audio codec Enhanced aacPlus is described in 10. 7 Enhanced aacPlus general audio codec: Enhanced aacPlus encoder Figure 2 shows a block diag
46、ram of the Enhanced aacPlus encoder. The input PCM time domain signal is first fed to a stereo-to-mono downmix unit, which is only applied if the input signal is stereo but the chosen audio encoding mode is selected to be mono. Next, the (mono or stereo) input time domain signal is fed to an IIR res
47、ampling filter in order to adjust the input sampling rate fsinto the best-suited sampling rate fsencfor the encoding process. The usage of the IIR resampler is only applied if the input signal sampling rate differs from the encoding sampling rate. The IIR resampler may either be run as a 3:2 downsam
48、pler (e.g. to downsample from 48 kHz to 32 kHz) or as a 1:2 upsampler (e.g. to upsample from 16 to 32 kHz). The Enhanced aacPlus encoder basically consists of the well-known AAC2(Advanced Audio Coding) waveform encoder, the SBR (Spectral Band Replication) high frequency reconstruction encoding tool
49、and the Parametric Stereo 2AAC has been standardized as recommended audio codec in 3GPP, Release 5 ETSI ETSI TS 126 401 V14.0.0 (2017-04)83GPP TS 26.401 version 14.0.0 Release 14encoding tool. The Enhanced aacPlus encoder is operating in a dual rate mode, whereas the SBR encoder operates at the encoding sampling rate fsencas delivered from the IIR resampler and the AAC encoder at half of this sampling rate fsenc/2. Consequently a 2:1 downsampler is present at the input to the AAC encoder. For an efficient implementation an II
