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Content for TS 26.403 Word version: 18.0.0

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3.1 Definitions 3.2 Symbols 3.3 Abbreviations 5.1 Overview 5.2 Stereo Preprocessing 5.3 Filterbank 5.4 Psychoacoustic Model 5.5 Tools 5.6 Quantization and coding

2 Normative references p. 5

3 Definitions, symbols and abbreviations p. 6

3.1 Definitions p. 6

3.2 Symbols p. 6

3.3 Abbreviations p. 6

4 Outline description p. 6

5 AAC Encoder p. 7

5.1 Overview p. 7

5.2 Stereo Preprocessing p. 8

5.3 Filterbank p. 8

5.4 Psychoacoustic Model p. 8

5.4.1 Blockswitching p. 8

5.4.2 Threshold Calculation p. 10

5.4.2.1 Calculation of the energy spectrum p. 10

5.4.2.2 From energy to threshold p. 11

5.4.2.3 Spreading p. 11

5.4.2.4 Threshold in quiet p. 11

5.4.2.5 Pre-echo control p. 11

5.4.3 Spreaded Energy Calculation p. 12

5.4.4 Grouping p. 12

5.5 Tools p. 12

5.5.1 Temporal Noise Shaping (TNS) p. 12

5.5.1.1 TNS detection p. 12

5.5.1.2 TNS Stereo Synchronization p. 13

5.5.1.3 TNS Order p. 13

5.5.1.4 TNS Filtering p. 13

5.5.1.5 Threshold modification p. 13

5.5.2 Mid/Side Stereo p. 13

5.6 Quantization and coding p. 14

5.6.1 Reduction of psychoacoustic requirements p. 14

5.6.1.1 Principle of the threshold reduction strategy p. 14

5.6.1.1.1 Addition of noise with equal loudness p. 14

5.6.1.1.2 Avoidance of spectral holes p. 14

5.6.1.1.3 Relation between bit demand and perceptual entropy p. 15

5.6.1.2 Calculation of Bit Demand p. 15

5.6.1.3 Calculation of the reduction value p. 17

5.6.1.3.1 Preparatory steps of the perceptual entropy calculation p. 18

5.6.1.3.2 Calculation of the desired perceptual entropy p. 18

5.6.1.3.3 Selection of the bands for avoidance of holes p. 18

5.6.1.3.4 First Estimation of the reduction value p. 18

5.6.1.3.5 Second Estimation of the reduction value p. 19

5.6.1.3.6 Final threshold modification by linearization p. 19

5.6.1.3.7 Further perceptual entropy reduction p. 20

5.6.1.3.8 Possible failures p. 20

5.6.2 Scalefactor determination p. 20

5.6.2.1 Scalefactor Estimation p. 21

5.6.2.2 Scalefactor Improvement by Quantization p. 21

5.6.2.3 Scalefactor Difference Reduction p. 21

5.6.2.4 Final scalefactor determination p. 22

5.6.3 Noiseless coding p. 22

5.6.4 Out of Bits Prevention p. 22

$ Change history p. 23