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Content for TS 26.290 Word version: 18.0.0

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5.1 Input signal pre-processing 5.2 Principle of the hybrid ACELP/TCX core encoding 5.3 Hybrid ACELP/TCX core encoding description 5.4 Mono Signal High-Band encoding (BWE) 5.5 Stereo signal encoding 5.6 Packetization

5 Functional description of the encoder p. 16

5.1 Input signal pre-processing p. 16

5.1.1 High Pass Filtering p. 16

5.1.2 Stereo Signal Downmixing/Bandsplitting p. 16

5.2 Principle of the hybrid ACELP/TCX core encoding p. 17

5.2.1 Timing chart of the ACELP and TCX modes p. 17

5.2.2 ACELP/TCX mode combinations and mode encoding p. 18

5.2.3 ACELP/TCX closed-loop mode selection p. 19

5.2.4 ACELP/TCX open-loop mode selection p. 20

5.3 Hybrid ACELP/TCX core encoding description p. 24

5.3.1 Pre-emphasis p. 24

5.3.2 LP analysis and interpolation p. 24

5.3.2.1 Windowing and auto correlation computation p. 24

5.3.2.2 Levinson Durbin algorithm p. 24

5.3.2.3 LP to ISP conversion p. 24

5.3.2.4 ISP to LP conversion p. 24

5.3.2.5 Quantization of the ISP coefficient p. 25

5.3.2.6 Interpolation of the ISPs p. 25

5.3.3 Perceptual weighting p. 25

5.3.4 ACELP Excitation encoder p. 25

5.3.4.1 Open loop pitch analysis p. 25

5.3.4.2 Impulse response computation p. 25

5.3.4.3 Target signal computation p. 26

5.3.4.4 Adaptive codebook p. 26

5.3.4.5 Algebraic codebook p. 26

5.3.4.5.1 Codebook structure p. 26

5.3.4.5.2 Pulse indexing p. 26

5.3.4.5.3 Codebook search p. 26

5.3.4.6 Quantization of the adaptive and fixed codebook gains p. 26

5.3.5 TCX Excitation encoder p. 27

5.3.5.1 TCX encoder block diagram p. 27

5.3.5.2 Computation of the target signal for transform coding p. 30

5.3.5.3 Zero-input response subtraction p. 30

5.3.5.4 Windowing of target signal p. 31

5.3.5.5 Transform p. 32

5.3.5.6 Spectrum pre-shaping p. 32

5.3.5.7 Split multi-rate lattice VQ p. 33

5.3.5.8 Spectrum de-shaping p. 38

5.3.5.9 Inverse transform p. 38

5.3.5.10 Gain optimization and quantization p. 38

5.3.5.11 Windowing for overlap-and-add p. 39

5.3.5.12 Memory update p. 39

5.3.5.13 Excitation signal computation p. 39

5.4 Mono Signal High-Band encoding (BWE) p. 39

5.5 Stereo signal encoding p. 42

5.5.1 Stereo Signal Low-Band Encoding p. 42

5.5.1.1 Principle p. 43

5.5.1.2 Signal Windowing p. 44

5.5.1.3 Pre-echo mode p. 44

5.5.1.4 Redundancy reduction p. 44

5.5.2 Stereo Signal Mid-Band Processing p. 44

5.5.2.1 Principle p. 44

5.5.2.2 Residual computation p. 45

5.5.2.3 Filter computation, smoothing and quantization p. 45

5.5.2.4 Channel energy matching p. 45

5.5.3 Stereo Signal High-Band Processing p. 46

5.6 Packetization p. 46

5.6.1 Packetization of TCX encoded parameters p. 46

5.6.1.1 Multiplexing principle for a single binary table p. 47

5.6.1.2 Multiplexing in case of multiple binary tables p. 48

5.6.2 Packetization procedure for all parameters p. 50

5.6.3 TCX gain multiplexing p. 52

5.6.4 Stereo Packetization p. 53