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Content for
TS 26.445
Word version: 16.1.1
1…
2…
5…
5.2…
5.4…
6…
7…
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
6.1.1.3.1
Anti-sparseness processing
6.1.1.3.2
Gain smoothing for noise enhancement
6.1.1.3.3
Pitch enhancer
Word‑p. 470
6.1.1.3.4
Music post processing
Word‑p. 471
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
6.1.5.2.1
SWB multi-mode FD BWE decoding
6.1.5.2.2
WB multi-mode FD BWE decoding
Word‑p. 503
6.1.5.3
Decoding of upper band at 64 kb/s
Word‑p. 511
6.1.5.3.1
Decoding in normal mode
6.1.5.3.2
Decoding in transient mode
Word‑p. 516
6.1.5.3.3
Windowing and frequency-to-time transformation
Word‑p. 518
6.1.5.3.4
Post-processing in temporal domain
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
6.2.4.4.1
ALDO to short transition
6.2.4.4.2
Short to ALDO transition
Word‑p. 582
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
6.3.3.2.1
Constrained CELP decoding and simplified BWE decoding
Word‑p. 587
6.3.3.2.1.1
Optimized cubic interpolation
6.3.3.2.2
HQ MDCT decoding with a modified synthesis window
Word‑p. 588
6.3.3.2.3
Cross-fading
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
6.3.4.6.1
Adaptive post-filtering
6.3.4.6.2
Bass post filter
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
6.3.7.1
Bandwidth switching detector
6.3.7.2
Super wideband switching to wideband
Word‑p. 591
6.3.7.2.1
TBE mode
6.3.7.2.2
Multi-mode FD BWE mode
Word‑p. 593
6.3.7.2.3
MDCT core
Word‑p. 594
6.3.7.3
Wideband switching to super wideband
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
6.7.3.3.1
Update of the noise levels for FD-CNG
6.7.3.3.2
Comfort noise generation in the frequency domain
6.7.3.3.3
Comfort noise generation in the time domain
6.7.3.3.4
FD-CNG decoder memory update
Word‑p. 609
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
6.8.1.4.1
Music post processing
6.8.1.4.2
Unvoiced and inactive post processing
Word‑p. 612
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
6.9.2.1
Decoding LTP parameters
6.9.2.2
LTP post filtering
Word‑p. 632
6.9.3
Complex low delay filter bank synthesis
Word‑p. 634
6.9.4
High pass filtering
Word‑p. 635