1、 ETSI TS 1Digital cellular telecoUniversal Mobile TelGeneral audio codEnhanced aaGe(3GPP TS 26.4TECHNICAL SPECIFICATION126 401 V13.0.0 (2016communications system (Phaelecommunications System (LTE; odec audio processing functiaacPlus general audio codec;General description .401 version 13.0.0 Release
2、 1316-01) hase 2+); (UMTS); ctions; c; 13) ETSI ETSI TS 126 401 V13.0.0 (2016-01)13GPP TS 26.401 version 13.0.0 Release 13Reference RTS/TSGS-0426401vd00 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 34
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12、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 identities o
13、r 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 not“,
14、“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 citatio
15、n. ETSI ETSI TS 126 401 V13.0.0 (2016-01)33GPP TS 26.401 version 13.0.0 Release 13Contents Intellectual Property Rights 2g3Foreword . 2g3Modal verbs terminology 2g3Foreword . 4g31 Scope 5g32 Normative references . 5g33 Abbreviations . 5g34 Outline description . 6g35 General . 6g36 Enhanced aacPlus g
16、eneral audio 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 10
17、g311 SBR Signalling in Payload formats 10g3Annex A (informative): Change history . 11g3History 12g3ETSI ETSI TS 126 401 V13.0.0 (2016-01)43GPP TS 26.401 version 13.0.0 Release 13Foreword The present document describes the Enhanced aacPlus general audio codec within the 3GPP system. The contents of t
18、he 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 version number as follows: Version x.y.z wher
19、e: 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, updates, etc. z the third digit is incremented
20、when editorial only changes have been incorporated in the specification; ETSI ETSI TS 126 401 V13.0.0 (2016-01)53GPP TS 26.401 version 13.0.0 Release 131 Scope This Telecommunication Standard (TS) describes the detailed mapping from an MPEG-4 bitstream containing Enhanced aacPlus coded audio to PCM
21、sample output. 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) al
22、so describes 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
23、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, the latest edition of the publication referred to applies. 1 3G
24、PP TS 26.410 : 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 gener
25、al audio 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, Parametri
26、c Coding 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 cod
27、ecs. 12 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 Efficien
28、cy AAC, 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 V13.0.0 (2016-01)63GPP TS 26.401
29、 version 13.0.0 Release 134 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,
30、 and references 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 En
31、hanced aacPlus 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 ba
32、ndwidth 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
33、 Enhanced 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 downmi
34、x a stereo 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 sampli
35、ng frequency 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 monophoni
36、c and stereophonic 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 3G
37、PP context. 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
38、 is not 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
39、 baseline 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. For terminals that are only capable of producing monophonic outpu
40、t the following additional statements apply: 1The HE-AAC Profile combines the AAC Low Complexity object type 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 bei
41、ng used, the maximum AAC sampling rate is restricted to 24 kHz whereas if SBR is not used the maximum AAC sampling rate is restricted to 48 kHz. ETSI ETSI TS 126 401 V13.0.0 (2016-01)73GPP TS 26.401 version 13.0.0 Release 13- implementation of the parametric stereo tool is not required. The decoder
42、would skip 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
43、tool since 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 Para
44、metric Stereo 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 gen
45、eral audio 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 bl
46、ock diagram 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
47、 IIR resampling 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
48、 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 encodi
49、ng tool and the Parametric Stereo encoding 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 2AAC has been standardized as recommended audio codec in 3GPP, Release 5 ETSI ETSI TS 126 401 V13.0.0 (2016-01)83GPP TS 26.401 version 13.0.0 Release 13fsenc/2. Consequently a 2:1 downsampler is present at the input to the AAC encoder. For an efficient implementati
