Content for TS 26.445 Word version: 16.1.1
6 Functional description of the Decoder
6.1 LP-based Decoding
6.2 MDCT Coding mode decoding
6.3 Switching coding modes in decoding
6.4 De-emphasis
6.5 Resampling to the output sampling frequency
6.6 Decoding of frame erasure concealment side information
6.7 Decoding in DTX/CNG operation
6.8 AMR-WB-interoperable modes
6.9 Common post-processing
6 Functional description of the Decoder Word‑p. 453
6.1 LP-based Decoding
6.1.1 General LP-based decoding
6.1.1.1 LSF decoding
6.1.1.1.1 General LSF decoding
6.1.1.1.2 LSF decoding for voiced coding mode at 16 kHz internal sampling frequency Word‑p. 456
6.1.1.2 Reconstruction of the excitation Word‑p. 458
6.1.1.2.1 Reconstruction of the excitation in GC and VC modes and high rate IC/UC modes
6.1.1.2.2 Reconstruction of the excitation in TC mode Word‑p. 465
6.1.1.2.3 Reconstruction of the excitation in UC mode at low rates
6.1.1.2.4 Reconstruction of the excitation in IC/UC mode at 9.6 kbps Word‑p. 467
6.1.1.2.5 Reconstruction of the excitation in GSC Word‑p. 468
6.1.1.3 Excitation post-processing Word‑p. 469
6.1.2 Source Controlled VBR decoding Word‑p. 478
6.1.3 Synthesis
6.1.4 Post-processing Word‑p. 479
6.1.4.1 Adaptive post-filtering
6.1.4.1.1 Long-term post-filter
6.1.4.1.2 Short-term post-filter Word‑p. 480
6.1.4.1.3 Post-filter NB parameters
6.1.4.1.4 Post-filter WB and SWB parameters Word‑p. 481
6.1.4.1.5 Tilt compensation
6.1.4.1.6 Adaptive gain control Word‑p. 482
6.1.4.2 Bass post-filter
6.1.5 Decoding of upper band for LP-based Coding Modes Word‑p. 485
6.1.5.1 Decoding Time-domain Bandwidth Extension
6.1.5.1.1 Generation of the upsampled version of the lowband excitation
6.1.5.1.2 Non-Linear Excitation Generation Word‑p. 486
6.1.5.1.3 De-quantization of high band parameters Word‑p. 487
6.1.5.1.4 LSP interpolation
6.1.5.1.5 Spectral flip in time domain
6.1.5.1.6 Down-sample using all-pass filters
6.1.5.1.7 Adaptive spectral whitening Word‑p. 488
6.1.5.1.8 Envelope modulated noise mixing
6.1.5.1.9 Spectral shaping of the noise added excitation Word‑p. 490
6.1.5.1.10 Post processing of the shaped excitation
6.1.5.1.11 Gain shape update
6.1.5.1.12 SHB synthesis Word‑p. 491
6.1.5.1.13 Core-switching and high-band memory updates Word‑p. 492
6.1.5.1.14 TEC/TFA post processing Word‑p. 493
6.1.5.1.15 Full-band synthesis Word‑p. 495
6.1.5.2 Multi-mode FD Bandwidth Extension decoding
6.1.5.3 Decoding of upper band at 64 kb/s Word‑p. 511
6.2 MDCT Coding mode decoding Word‑p. 521
6.2.1 General MDCT decoding
6.2.2 MDCT based TCX
6.2.2.1 Rate dependent configurations
6.2.2.2 Init module parameters
6.2.2.2.1 TCX block configuration
6.2.2.2.2 LPC parameter
6.2.2.2.3 PLC Wavefrom adjustment Word‑p. 522
6.2.2.2.4 Global Gain
6.2.2.2.5 Noise fill parameter Word‑p. 523
6.2.2.2.6 LTP
6.2.2.2.7 TNS parameter
6.2.2.2.8 Harmonic model
6.2.2.2.9 IGF bit stream reader
6.2.2.2.10 Spectral data Word‑p. 526
6.2.2.2.11 Residual bits
6.2.2.3 Decoding process Word‑p. 527
6.2.2.3.1 Arithmetic decoder
6.2.2.3.2 Adaptive low frequency de-emphasis Word‑p. 528
6.2.2.3.3 Global gain decoding Word‑p. 529
6.2.2.3.4 Residual bits decoding
6.2.2.3.5 TCX formant enhancement Word‑p. 530
6.2.2.3.6 Noise Filling Word‑p. 531
6.2.2.3.7 Apply global gain and LPC shaping in MDCT domain Word‑p. 532
6.2.2.3.8 IGF apply Word‑p. 533
6.2.2.3.9 Inverse window grouping (TCX5 separation) Word‑p. 538
6.2.2.3.10 Temporal Noise Shaping Word‑p. 539
6.2.2.3.11 IGF temporal flattening
6.2.3 High Quality MDCT decoder (HQ) Word‑p. 540
6.2.3.1 Low-rate HQ decoder
6.2.3.1.1 Mode decoding
6.2.3.1.2 Energy Envelope decoding
6.2.3.1.3 Spectral coefficients decoding Word‑p. 542
6.2.3.2 High-rate HQ decoder Word‑p. 552
6.2.3.2.1 Normal Mode
6.2.3.2.2 Transient Mode Word‑p. 561
6.2.3.2.3 Harmonic Mode
6.2.3.2.4 HVQ Word‑p. 564
6.2.3.2.5 Generic Mode Word‑p. 565
6.2.3.2.6 PVQ decoding and de-indexing Word‑p. 570
6.2.4 Frequency-to-time transformation Word‑p. 572
6.2.4.1 Long block transformation (ALDO window)
6.2.4.1.1 eDCT
6.2.4.1.2 Unfolding and windowing
6.2.4.1.3 Overlap-add Word‑p. 573
6.2.4.1.4 Pre-echo attenuation Word‑p. 574
6.2.4.2 Transient location dependent overlap and transform length Word‑p. 580
6.2.4.3 Short block transformation
6.2.4.3.1 Short window transform in TDA domain
6.2.4.3.2 Short window transform for MDCT based TCX Word‑p. 581
6.2.4.4 Special window transitions
6.2.4.5 Low Rate MDCT Synthesis
6.3 Switching coding modes in decoding
6.3.1 General description
6.3.2 MDCT coding mode to CELP coding mode Word‑p. 583
6.3.2.1 MDCT to CELP transition 1 (MC1)
6.3.2.2 MDCT to CELP transition 2 (MC2) Word‑p. 584
6.3.2.3 MDCT to CELP transition 3 (MC3)
6.3.3 CELP coding mode to MDCT coding mode
6.3.3.1 CELP coding mode to MDCT based TCX coding mode Word‑p. 585
6.3.3.2 CELP coding mode to HQ MDCT coding mode Word‑p. 586
6.3.4 Internal sampling rate switching
6.3.4.1 Reset of LPC memory
6.3.4.2 Conversion of LP filter between 12.8 and 16 kHz internal sampling rates Word‑p. 589
6.3.4.3 Extrapolation of LP filter
6.3.4.4 Update of CELP synthesis memories
6.3.4.5 Update of CELP decoded past signal
6.3.4.6 Post-processing
6.3.4.7 CLDFB
6.3.5 EVS primary modes and AMR-WB IO Word‑p. 590
6.3.5.1 Switching from primary modes to AMR-WB IO
6.3.5.2 Switching from AMR-WB IO mode to primary modes
6.3.6 Rate switching
6.3.6.1 Rate switching along with internal sampling rate switching
6.3.6.2 Rate switching along with coding mode switching
6.3.6.3 Adaptive post-filter reset and smoothing
6.3.7 Bandwidth switching
6.4 De-emphasis
6.5 Resampling to the output sampling frequency
6.6 Decoding of frame erasure concealment side information
6.7 Decoding in DTX/CNG operation Word‑p. 595
6.7.1 Overview
6.7.2 Decoding for LP-CNG
6.7.2.1 LP-CNG decoding Overview
6.7.2.1.1 CNG parameter updates in active periods
6.7.2.1.2 DTX-hangover based parameter analysis in LP-CNG mode Word‑p. 596
6.7.2.1.3 LP-CNG low-band energy decoding Word‑p. 598
6.7.2.1.4 LP-CNG low-band filter parameters decoding
6.7.2.1.5 LP-CNG low-band excitation generation
6.7.2.1.6 LP-CNG low-band synthesis Word‑p. 600
6.7.2.1.7 LP-CNG high-band decoding and synthesis
6.7.2.2 Memory update Word‑p. 602
6.7.3 Decoding for FD-CNG
6.7.3.1 Decoding SID frames in FD-CNG
6.7.3.1.1 SID parameters decoding Word‑p. 603
6.7.3.1.2 SID parameters interpolation
6.7.3.1.3 LPC estimation from the interpolated SID parameters Word‑p. 604
6.7.3.2 Noise tracking during active frames in FD-CNG
6.7.3.2.1 Spectral partition energies
6.7.3.2.2 FD-CNG noise estimation Word‑p. 605
6.7.3.2.3 Noise shaping in FD-CNG
6.7.3.3 Noise generation for SID or zero frames in FD-CNG Word‑p. 607
6.8 AMR-WB-interoperable modes Word‑p. 610
6.8.1 Decoding and speech synthesis
6.8.1.1 Excitation decoding
6.8.1.2 Excitation post-processing Word‑p. 611
6.8.1.2.1 Anti-sparseness processing
6.8.1.2.2 Gain smoothing for noise enhancement
6.8.1.2.3 Pitch enhancer
6.8.1.3 Synthesis filtering
6.8.1.4 Music and Unvoiced/inactive Post-processing
6.8.1.5 Synthesis filtering and overwriting the current CELP synthesis Word‑p. 615
6.8.1.6 Formant post-filter
6.8.1.7 Comfort noise addition
6.8.1.8 Bass post-filter
6.8.2 Resampling Word‑p. 616
6.8.3 High frequency band
6.8.3.1 Preliminary estimation steps
6.8.3.1.1 Estimation of tilt, figure of merit and voice factors Word‑p. 617
6.8.3.1.2 Estimation of sub-frame gains based on LP spectral envelopes Word‑p. 618
6.8.3.2 Generation of high-band excitation Word‑p. 621
6.8.3.2.1 DCT
6.8.3.2.2 High band generation
6.8.3.2.3 Extraction of tonal and ambiance components Word‑p. 623
6.8.3.2.4 Recombination Word‑p. 624
6.8.3.2.5 Filtering in DCT domain Word‑p. 625
6.8.3.2.6 Inverse DCT Word‑p. 626
6.8.3.2.7 Gain computation and scaling of excitation
6.8.3.3 LP filter for the high frequency band Word‑p. 628
6.8.3.4 High band synthesis
6.8.4 CNG decoding
6.9 Common post-processing Word‑p. 629
6.9.1 Comfort noise addition
6.9.1.1 Noisy speech detection
6.9.1.2 Noise estimation for CNA Word‑p. 630
6.9.1.2.1 CNA noise estimation in DTX-on mode when FD-CNG is triggered
6.9.1.2.2 CNA noise estimation in DTX-on mode when LP-CNG is triggered
6.9.1.2.3 CNA noise estimation in DTX-off mode
6.9.1.3 Noise generation in the FFT domain and addition in the time domain
6.9.1.4 Noise generation and addition in the MDCT domain Word‑p. 631
6.9.2 Long term prediction processing
6.9.3 Complex low delay filter bank synthesis Word‑p. 634
6.9.4 High pass filtering Word‑p. 635
