1、 ETSI TS 126 401 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; General description (3GPP TS 26.401 version 15.0.0 Release 15)
2、 TECHNICAL SPECIFICATION ETSI ETSI TS 126 401 V15.0.0 (2018-07)13GPP TS 26.401 version 15.0.0 Release 15Reference RTS/TSGS-0426401vf00 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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9、 trademarks registered and owned by the GSM Association. ETSI ETSI TS 126 401 V15.0.0 (2018-07)23GPP TS 26.401 version 15.0.0 Release 15Intellectual Property Rights Essential patents IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information per
10、taining 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 Secre
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12、n the ETSI Web server) which are, or may be, or may become, essential to the present document. Trademarks The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners. ETSI claims no ownership of these except for any which are indicated as being
13、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 This Technical Specification
14、 (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 corresponding ETSI deliverables. The
15、 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“ are to be interpreted as de
16、scribed 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 126 401 V15.0.0 (2018-07)33GPP TS 26.401 version 15.0.0 Release 15Contents Intellectual Prope
17、rty Rights 2g3Foreword . 2g3Modal verbs terminology 2g3Foreword . 4g31 Scope 5g32 Normative references . 5g33 Abbreviations . 5g34 Outline description . 6g35 General . 6g36 Enhanced aacPlus general audio codec: ANSI-C code 7g37 Enhanced aacPlus general audio codec: Enhanced aacPlus encoder . 7g38 En
18、hanced 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 Signalling in Payload formats 10g3Annex A (informative): Change history . 11g3History 12g3ETSI ETSI
19、TS 126 401 V15.0.0 (2018-07)43GPP TS 26.401 version 15.0.0 Release 15Foreword The present document describes the Enhanced 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 approva
20、l. 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 first digit: 1 presented to TSG for information; 2 presented to TSG for approval; 3 Indicates TSG ap
21、proved 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 editorial only changes have been incorporated in the specification; ETSI ETSI TS 126 401 V15.0.0 (2018-0
22、7)53GPP TS 26.401 version 15.0.0 Release 151 Scope This Telecommunication Standard (TS) describes the detailed mapping from an MPEG-4 bitstream containing Enhanced aacPlus coded audio to PCM sample output. The Enhanced aacPlus audio codec is based on the AAC, SBR and Parametric Stereo coding tools d
23、efined 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 describes the detailed mapping from a PCM sample input to an MPEG-4 bitstream containing Enhanced aacPlus
24、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 and the publications are listed hereafter. For dated references, subsequent amendments to or revisio
25、ns 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 26.410 : Enhanced aacPlus general audio codec; Floating-point ANSI-C Code. 2 3GPP TS 26.403 : Enhanced
26、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 codec; Encoder Specification Parametric Stereo part. 5 ISO/IEC 14496-3:2001, Information technology
27、- 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 for High Quality Audio. 9 3GPP TS 26.402: Enhanced aacPlus general audio codec; Additional Decoder T
28、ools. 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 ISO/IEC 14496-3:2001/Amd.2:2004/DCOR 1. 3 Abbreviations For the purposes of this TS, the following ab
29、breviations 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, the combination of MPEG-4 AAC and MPEG-4 Bandwidth extension (SBR) Enhanced aacPlus MPEG-4 High Effic
30、iency AAC plus MPEG-4 Parametric StereoMDCT Modified Discrete Cosine Transform QMF Quadrature Mirror Filter SBR Spectral Band Replication ETSI ETSI TS 126 401 V15.0.0 (2018-07)63GPP TS 26.401 version 15.0.0 Release 154 Outline description This TS is structured as follows: Section 5 gives a general o
31、verview 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 references the relevant detailed technical description documents. Section 8 gives a more detailed overvi
32、ew 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 aacPlus decoder that are not part of the cited ISO standards, and references the relevant detailed tec
33、hnical 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 extension technique offering substantial coding gain in combination with AAC, and Parametric Stereo e
34、nables 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 Enhanced aacPlus decoder: - Error concealment tools for AAC, SBR, and Parametric Stereo make the decoder rob
35、ust 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 stereo bitstream. For the AAC part this is done in the time domain after the stereo decoding but for SBR
36、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 frequency different than what was supplied in the bitstream. This gives for example handsets with a D/A co
37、nverter 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 stereophonic coding. For stereophonic coding two stereo modes are used: parametric stereo for low bitra
38、tes 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 context. From the ISO standards the following subset shall be used: The Enhanced aacPlus general audio cod
39、ec 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 supported); For terminals supporting stereophonic output the following additional statements apply: -
40、 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 baseline version of the parametric stereo coding tool in direct combination with the SBR tool, as defined in
41、 8. - for M/S stereo bitstreams, it is recommended that the Enhanced aacPlus decoder operates the SBR tool in Low Power mode. For terminals that are only capable of producing monophonic output the following additional statements apply: 1The HE-AAC Profile combines the AAC Low Complexity object type
42、plus the 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 sam
43、pling rate is restricted to 48 kHz. ETSI ETSI TS 126 401 V15.0.0 (2018-07)73GPP TS 26.401 version 15.0.0 Release 15- implementation of the parametric stereo tool is not required. The decoder would skip the parametric stereo data and only decode the mono portion of the signal. - the stereo-to-mono-do
44、wnmix 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 since it allows for reduced computational complexity and lower memory requirements Figure 1 illustrates
45、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 Stereo tool. Enhanced aacPlus is thus a true superset of aacPlus and AAC. aacPlus(= MPEG-4 High Effici
46、ency 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 audio codec: ANSI-C code The Floating-point ANSI C-code of the general audio codec Enhanced aacPlus is d
47、escribed 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 diagram of the Enhanced aacPlus encoder. The input PCM time domain signal is first fed to a stereo-to-mon
48、o 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 resampling filter in order to adjust the input sampling rate fsinto the best-suited sampling rate fsencf
49、or 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 downsampler (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 and the Parametric Stereo encoding
