ETSI TS 102 366 V1.4.1 (2017-09)

Digital Audio Compression (AC-3, Enhanced AC-3) Standard

RTS/JTC-041

General Information

• Status: Published
• Publication Date: 19-Sep-2017
• Technical Committee: BROADCAS - EBU/CENELEC/ETSI on Broadcasting
• Current Stage: 12 - Completion
• Due Date: 21-Sep-2017
• Completion Date: 20-Sep-2017

Standards Content (Sample)

ETSI TS 102 366 V1.4.1 (2017-09)






TECHNICAL SPECIFICATION
Digital Audio Compression
(AC-3, Enhanced AC-3) Standard

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2 ETSI TS 102 366 V1.4.1 (2017-09)



Reference
RTS/JTC-041
Keywords
audio, broadcasting, coding, digital
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3 ETSI TS 102 366 V1.4.1 (2017-09)
Contents
Intellectual Property Rights . 17
Foreword . 17
Modal verbs terminology . 17
Introduction . 18
1 Scope . 21
2 References . 21
2.1 Normative references . 21
2.2 Informative references . 21
3 Definitions and abbreviations . 22
3.1 Definitions . 22
3.2 Abbreviations . 24
4 Bit stream syntax . 27
4.1 Synchronization frame . 27
4.2 Semantics of syntax specification. 27
4.3 Syntax specification . 28
4.3.0 AC-3_bit_stream and syncframe . 28
4.3.1 syncinfo - Synchronization information . 28
4.3.2 bsi - Bit stream information . 28
4.3.3 audblk - Audio block . 29
4.3.4 auxdata - Auxiliary data . 32
4.3.5 errorcheck - Error detection code . 32
4.4 Description of bit stream elements . 32
4.4.0 Introduction. 32
4.4.1 syncinfo - Synchronization information . 32
4.4.1.1 syncword - Synchronization word - 16 bits . 32
4.4.1.2 crc1 - Cyclic redundancy check 1 bit to 16 bits . 32
4.4.1.3 fscod - Sample rate code - 2 bits . 33
4.4.1.4 frmsizecod - Frame size code - 6 bits . 33
4.4.2 bsi - Bit stream information . 33
4.4.2.1 bsid - Bit stream identification - 5 bits . 33
4.4.2.2 bsmod - Bit stream mode - 3 bits . 33
4.4.2.3 acmod - Audio coding mode - 3 bits . 33
4.4.2.4 cmixlev - Centre mix level - 2 bits . 34
4.4.2.5 surmixlev - Surround mix level - 2 bits . 34
®
4.4.2.6 dsurmod - Dolby Surround mode - 2 bits . 34
4.4.2.7 lfeon - Low frequency effects channel on - 1 bit . 35
4.4.2.8 dialnorm - Dialogue normalization - 5 bits . 35
4.4.2.9 compre - Compression gain word exists - 1 bit . 35
4.4.2.10 compr - Compression gain word - 8 bits . 35
4.4.2.11 langcode - Language code exists - 1 bit . 35
4.4.2.12 langcod - Language code - 8 bits . 35
4.4.2.13 audprodie - Audio production information exists - 1 bit . 35
4.4.2.14 mixlevel - Mixing level - 5 bits . 36
4.4.2.15 roomtyp - Room type - 2 bits . 36
4.4.2.16 dialnorm2 - Dialogue normalization, Ch2 - 5 bits . 36
4.4.2.17 compr2e - Compression gain word exists, Ch2 - 1 bit . 36
4.4.2.18 compr2 - Compression gain word, Ch2 - 8 bits. 36
4.4.2.19 langcod2e - Language code exists, Ch2 - 1 bit . 36
4.4.2.20 langcod2 - Language code, Ch2 - 8 bits . 36
4.4.2.21 audprodi2e - Audio production information exists, Ch2 - 1 bit . 36
4.4.2.22 mixlevel2 - Mixing level, Ch2 - 5 bits . 36
4.4.2.23 roomtyp2 - Room type, Ch2 - 2 bits . 37
4.4.2.24 copyrightb - Copyright bit - 1 bit . 37
ETSI

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4 ETSI TS 102 366 V1.4.1 (2017-09)
4.4.2.25 origbs - Original bit stream - 1 bit . 37
4.4.2.26 timecod1e, timecod2e - Time code (first and second) halves exists - 2 bits . 37
4.4.2.27 timecod1 - Time code first half - 14 bits . 37
4.4.2.28 timecod2 - Time code second half - 14 bits . 37
4.4.2.29 addbsie - Additional bit stream information exists - 1 bit . 37
4.4.2.30 addbsil - Additional bit stream information length - 6 bits . 37
4.4.2.31 addbsi - Additional bit stream information - ((addbsil + 1) x 8) bits . 37
4.4.3 audblk - Audio block . 38
4.4.3.1 blksw[ch] - Block switch flag - 1 bit . 38
4.4.3.2 dithflag[ch] - Dither flag - 1 bit . 38
4.4.3.3 dynrnge - Dynamic range gain word exists - 1 bit . 38
4.4.3.4 dynrng - Dynamic range gain word - 8 bits . 38
4.4.3.5 dynrng2e - Dynamic range gain word exists, Ch2 - 1 bit . 38
4.4.3.6 dynrng2 - dynamic range gain word, Ch2 - 8 bits . 38
4.4.3.7 cplstre - Coupling strategy exists - 1 bit . 38
4.4.3.8 cplinu - Coupling in use - 1 bit . 38
4.4.3.9 chincpl[ch] - Channel in coupling - 1 bit . 38
4.4.3.10 phsflginu - Phase flags in use - 1 bit . 38
4.4.3.11 cplbegf - Coupling begin frequency code - 4 bits . 39
4.4.3.12 cplendf - Coupling end frequency code - 4 bits . 39
4.4.3.13 cplbndstrc[sbnd] - Coupling band structure - 1 bit . 39
4.4.3.14 cplcoe[ch] - Coupling coordinates exist - 1 bit . 39
4.4.3.15 mstrcplco[ch] - Master coupling coordinate - 2 bits . 40
4.4.3.16 cplcoexp[ch][bnd] - Coupling coordinate exponent - 4 bits . 40
4.4.3.17 cplcomant[ch][bnd] - Coupling coordinate mantissa - 4 bits . 40
4.4.3.18 phsflg[bnd] - Phase flag - 1 bit . 40
4.4.3.19 rematstr - Rematrixing strategy - 1 bit . 40
4.4.3.20 rematflg[rbnd] - Rematrix flag - 1 bit . 40
4.4.3.21 cplexpstr - Coupling exponent strategy - 2 bits . 40
4.4.3.22 chexpstr[ch] - Channel exponent strategy - 2 bits . 41
4.4.3.23 lfeexpstr - Low frequency effects channel exponent strategy - 1 bit . 41
4.4.3.24 chbwcod[ch] - Channel bandwidth code - 6 bits . 41
4.4.3.25 cplabsexp - Coupling absolute exponent - 4 bits . 41
4.4.3.26 cplexps[grp] - Coupling exponents - 7 bits . 41
4.4.3.27 exps[ch][grp] - Channel exponents - 4 bits or 7 bits . 41
4.4.3.28 gainrng[ch] - Channel gain range code - 2 bits . 41
4.4.3.29 lfeexps[grp] - Low frequency effects channel exponents - 4 bits or 7 bits . 41
4.4.3.30 baie - Bit allocation information exists - 1 bit . 41
4.4.3.31 sdcycod - Slow decay code - 2 bits . 41
4.4.3.32 fdcycod - Fast decay code - 2 bits . 42
4.4.3.33 sgaincod - Slow gain code - 2 bits . 42
4.4.3.34 dbpbcod - dB per bit code - 2 bits . 42
4.4.3.35 floorcod - Masking floor code - 3 bits . 42
4.4.3.36 snroffste - SNR offset exists - 1 bit . 42
4.4.3.37 csnroffst - Coarse SNR offset - 6 bits . 42
4.4.3.38 cplfsnroffst - Coupling fine SNR offset - 4 bits . 42
4.4.3.39 cplfgaincod - Coupling fast gain code - 3 bits . 42
4.4.3.40 fsnroffst[ch] - Channel fine SNR offset - 4 bits . 42
4.4.3.41 fgaincod[ch] - Channel fast gain code - 3 bits . 42
4.4.3.42 lfefsnroffst - Low frequency effects channel fine SNR offset - 4 bits . 42
4.4.3.43 lfefgaincod - Low frequency effects channel fast gain code - 3 bits . 42
4.4.3.44 cplleake - Coupling leak initialization exists - 1 bit . 42
4.4.3.45 cplfleak - Coupling fast leak initialization - 3 bits . 43
4.4.3.46 cplsleak - Coupling slow leak initialization - 3 bits . 43
4.4.3.47 deltbaie - Delta bit allocation information exists - 1 bit . 43
4.4.3.48 cpldeltbae - Coupling delta bit allocation exists - 2 bits. 43
4.4.3.49 deltbae[ch] - Delta bit allocation exists - 2 bits . 43
4.4.3.50 cpldeltnseg - Coupling delta bit allocation number of segments - 3 bits . 43
4.4.3.51 cpldeltoffst[seg] - Coupling delta bit allocation offset - 5 bits . 43
4.4.3.52 cpldeltlen[seg] - Coupling delta bit allocation length - 4 bits . 43
4.4.3.53 cpldeltba[seg] - Coupling delta bit allocation - 3 bits . 43
4.4.3.54 deltnseg[ch] - Channel delta bit allocation number of segments - 3 bits . 44
ETSI

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5 ETSI TS 102 366 V1.4.1 (2017-09)
4.4.3.55 deltoffst[ch][seg] - Channel delta bit allocation offset - 5 bits . 44
4.4.3.56 deltlen[ch][seg] - Channel delta bit allocation length - 4 bits . 44
4.4.3.57 deltba[ch][seg] - Channel delta bit allocation - 3 bits . 44
4.4.3.58 skiple - Skip length exists - 1 bit . 44
4.4.3.59 skipl - Skip length - 9 bits . 44
4.4.3.60 skipfld - Skip field - (skipl x 8) bits . 44
4.4.3.61 chmant[ch][bin] - Channel mantissas - 0 bits to 16 bits . 44
4.4.3.62 cplmant[bin] - Coupling mantissas - 0 bits to 16 bits . 45
4.4.3.63 lfemant[bin] - Low frequency effects channel mantissas - 0 bits to 16 bits . 45
4.4.4 auxdata - Auxiliary data field . 45
4.4.4.0 Introduction . 45
4.4.4.1 auxbits - Auxiliary data bits - nauxbits bits . 45
4.4.4.2 auxdatal - Auxiliary data length - 14 bits . 46
4.4.4.3 auxdatae - Auxiliary data exists - 1 bit . 46
4.4.5 errorcheck - Frame error detection field . 46
4.4.5.1 crcrsv - CRC reserved bit - 1 bit . 46
4.4.5.2 crc2 - Cyclic redundancy check 2 - 16 bits . 46
4.5 Bit stream constraints . 46
5 Decoding the AC-3 bit stream . 47
5.1 Introduction . 47
5.2 Summary of the decoding process . 47
5.2.1 Input bit stream . 47
5.2.1.0 Introduction . 47
5.2.1.1 Continuous or burst input . 47
5.2.1.2 Byte or word alignment . 47
5.2.2 Synchronization and error detection . 48
5.2.3 Unpack BSI, side information. 49
5.2.4 Decode exponents . 50
5.2.5 Bit allocation . 50
5.2.6 Process mantissas . 50
5.2.7 Decoupling . 50
5.2.8 Rematrixing . 50
5.2.9 Dynamic range compression . 50
5.2.10 Inverse transform . 50
5.2.11 Window, overlap/add . 51
5.2.12 Downmixing . 51
5.2.13 PCM output buffer . 51
5.2.14 Output PCM . 51
6 Algorithmic details . 51
6.0 Introduction . 51
6.1 Exponent coding . 51
6.1.1 Overview . 51
6.1.2 Exponent strategy . 52
6.1.3 Exponent decoding . 53
6.2 Bit allocation . 55
6.2.1 Overview . 55
6.2.2 Parametric bit allocation . 56
6.2.2.0 Introduction . 56
6.2.2.1 Initialization . 56
6.2.2.2 Exponent mapping into psd . 57
6.2.2.3 psd integration . 57
6.2.2.4 Compute excitation function . 58
6.2.2.5 Compute masking curve . 59
6.2.2.6 Apply delta bit allocation . 60
6.2.2.7 Compute bit allocation . 60
6.2.3 Bit allocation tables . 61
6.3 Quantization and decoding of mantissas . 65
6.3.1 Overview . 65
6.3.2 Expansion of mantissas for asymmetric quantization (6 ≤ bap ≤ 15) . 66
6.3.3 Expansion of mantissas for symmetrical quantization (1 ≤ bap ≤ 5) . 66
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6 ETSI TS 102 366 V1.4.1 (2017-09)
6.3.4 Dither for zero bit mantissas (bap = 0) . 66
6.3.5 Ungrouping of mantissas . 68
6.4 Channel coupling .
...