Tech-
invite
3GPP
space
IETF
space
21
22
23
24
25
26
27
28
29
31
32
33
34
35
36
37
38
4‑5x
Content for
TS 26.445
Word version: 18.0.0
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
p. 453
6.1
LP-based Decoding
p. 453
6.1.1
General LP-based decoding
p. 453
6.1.1.1
LSF decoding
p. 453
6.1.1.1.1
General LSF decoding
p. 453
6.1.1.1.2
LSF decoding for voiced coding mode at 16 kHz internal sampling frequency
p. 456
6.1.1.2
Reconstruction of the excitation
p. 458
6.1.1.2.1
Reconstruction of the excitation in GC and VC modes and high rate IC/UC modes
p. 458
6.1.1.2.2
Reconstruction of the excitation in TC mode
p. 465
6.1.1.2.3
Reconstruction of the excitation in UC mode at low rates
p. 465
6.1.1.2.4
Reconstruction of the excitation in IC/UC mode at 9.6 kbps
p. 467
6.1.1.2.5
Reconstruction of the excitation in GSC
p. 468
6.1.1.3
Excitation post-processing
p. 469
6.1.1.3.1
Anti-sparseness processing
p. 469
6.1.1.3.2
Gain smoothing for noise enhancement
p. 469
6.1.1.3.3
Pitch enhancer
p. 470
6.1.1.3.4
Music post processing
p. 471
6.1.2
Source Controlled VBR decoding
p. 478
6.1.3
Synthesis
p. 478
6.1.4
Post-processing
p. 479
6.1.4.1
Adaptive post-filtering
p. 479
6.1.4.1.1
Long-term post-filter
p. 479
6.1.4.1.2
Short-term post-filter
p. 480
6.1.4.1.3
Post-filter NB parameters
p. 480
6.1.4.1.4
Post-filter WB and SWB parameters
p. 481
6.1.4.1.5
Tilt compensation
p. 481
6.1.4.1.6
Adaptive gain control
p. 482
6.1.4.2
Bass post-filter
p. 482
6.1.5
Decoding of upper band for LP-based Coding Modes
p. 485
6.1.5.1
Decoding Time-domain Bandwidth Extension
p. 485
6.1.5.1.1
Generation of the upsampled version of the lowband excitation
p. 485
6.1.5.1.2
Non-Linear Excitation Generation
p. 486
6.1.5.1.3
De-quantization of high band parameters
p. 487
6.1.5.1.4
LSP interpolation
p. 487
6.1.5.1.5
Spectral flip in time domain
p. 487
6.1.5.1.6
Down-sample using all-pass filters
p. 487
6.1.5.1.7
Adaptive spectral whitening
p. 488
6.1.5.1.8
Envelope modulated noise mixing
p. 488
6.1.5.1.9
Spectral shaping of the noise added excitation
p. 490
6.1.5.1.10
Post processing of the shaped excitation
p. 490
6.1.5.1.11
Gain shape update
p. 490
6.1.5.1.12
SHB synthesis
p. 491
6.1.5.1.13
Core-switching and high-band memory updates
p. 492
6.1.5.1.14
TEC/TFA post processing
p. 493
6.1.5.1.15
Full-band synthesis
p. 495
6.1.5.2
Multi-mode FD Bandwidth Extension decoding
p. 495
6.1.5.2.1
SWB multi-mode FD BWE decoding
p. 495
6.1.5.2.2
WB multi-mode FD BWE decoding
p. 503
6.1.5.3
Decoding of upper band at 64 kb/s
p. 511
6.1.5.3.1
Decoding in normal mode
p. 511
6.1.5.3.2
Decoding in transient mode
p. 516
6.1.5.3.3
Windowing and frequency-to-time transformation
p. 518
6.1.5.3.4
Post-processing in temporal domain
p. 518
6.2
MDCT Coding mode decoding
p. 521
6.2.1
General MDCT decoding
p. 521
6.2.2
MDCT based TCX
p. 521
6.2.2.1
Rate dependent configurations
p. 521
6.2.2.2
Init module parameters
p. 521
6.2.2.2.1
TCX block configuration
p. 521
6.2.2.2.2
LPC parameter
p. 521
6.2.2.2.3
PLC Wavefrom adjustment
p. 522
6.2.2.2.4
Global Gain
p. 522
6.2.2.2.5
Noise fill parameter
p. 523
6.2.2.2.6
LTP
p. 523
6.2.2.2.7
TNS parameter
p. 523
6.2.2.2.8
Harmonic model
p. 523
6.2.2.2.9
IGF bit stream reader
p. 523
6.2.2.2.10
Spectral data
p. 526
6.2.2.2.11
Residual bits
p. 526
6.2.2.3
Decoding process
p. 527
6.2.2.3.1
Arithmetic decoder
p. 527
6.2.2.3.2
Adaptive low frequency de-emphasis
p. 528
6.2.2.3.3
Global gain decoding
p. 529
6.2.2.3.4
Residual bits decoding
p. 529
6.2.2.3.5
TCX formant enhancement
p. 530
6.2.2.3.6
Noise Filling
p. 531
6.2.2.3.7
Apply global gain and LPC shaping in MDCT domain
p. 532
6.2.2.3.8
IGF apply
p. 533
6.2.2.3.9
Inverse window grouping (TCX5 separation)
p. 538
6.2.2.3.10
Temporal Noise Shaping
p. 539
6.2.2.3.11
IGF temporal flattening
p. 539
6.2.3
High Quality MDCT decoder (HQ)
p. 540
6.2.3.1
Low-rate HQ decoder
p. 540
6.2.3.1.1
Mode decoding
p. 540
6.2.3.1.2
Energy Envelope decoding
p. 540
6.2.3.1.3
Spectral coefficients decoding
p. 542
6.2.3.2
High-rate HQ decoder
p. 552
6.2.3.2.1
Normal Mode
p. 552
6.2.3.2.2
Transient Mode
p. 561
6.2.3.2.3
Harmonic Mode
p. 561
6.2.3.2.4
HVQ
p. 564
6.2.3.2.5
Generic Mode
p. 565
6.2.3.2.6
PVQ decoding and de-indexing
p. 570
6.2.4
Frequency-to-time transformation
p. 572
6.2.4.1
Long block transformation (ALDO window)
p. 572
6.2.4.1.1
eDCT
p. 572
6.2.4.1.2
Unfolding and windowing
p. 572
6.2.4.1.3
Overlap-add
p. 573
6.2.4.1.4
Pre-echo attenuation
p. 574
6.2.4.2
Transient location dependent overlap and transform length
p. 580
6.2.4.3
Short block transformation
p. 580
6.2.4.3.1
Short window transform in TDA domain
p. 580
6.2.4.3.2
Short window transform for MDCT based TCX
p. 581
6.2.4.4
Special window transitions
p. 581
6.2.4.4.1
ALDO to short transition
p. 581
6.2.4.4.2
Short to ALDO transition
p. 582
6.2.4.5
Low Rate MDCT Synthesis
p. 582
6.3
Switching coding modes in decoding
p. 582
6.3.1
General description
p. 582
6.3.2
MDCT coding mode to CELP coding mode
p. 583
6.3.2.1
MDCT to CELP transition 1 (MC1)
p. 583
6.3.2.2
MDCT to CELP transition 2 (MC2)
p. 584
6.3.2.3
MDCT to CELP transition 3 (MC3)
p. 584
6.3.3
CELP coding mode to MDCT coding mode
p. 584
6.3.3.1
CELP coding mode to MDCT based TCX coding mode
p. 585
6.3.3.2
CELP coding mode to HQ MDCT coding mode
p. 586
6.3.3.2.1
Constrained CELP decoding and simplified BWE decoding
p. 587
6.3.3.2.1.1
Optimized cubic interpolation
p. 587
6.3.3.2.2
HQ MDCT decoding with a modified synthesis window
p. 588
6.3.3.2.3
Cross-fading
p. 588
6.3.4
Internal sampling rate switching
p. 588
6.3.4.1
Reset of LPC memory
p. 588
6.3.4.2
Conversion of LP filter between 12.8 and 16 kHz internal sampling rates
p. 589
6.3.4.3
Extrapolation of LP filter
p. 589
6.3.4.4
Update of CELP synthesis memories
p. 589
6.3.4.5
Update of CELP decoded past signal
p. 589
6.3.4.6
Post-processing
p. 589
6.3.4.6.1
Adaptive post-filtering
p. 589
6.3.4.6.2
Bass post filter
p. 589
6.3.4.7
CLDFB
p. 589
6.3.5
EVS primary modes and AMR-WB IO
p. 590
6.3.5.1
Switching from primary modes to AMR-WB IO
p. 590
6.3.5.2
Switching from AMR-WB IO mode to primary modes
p. 590
6.3.6
Rate switching
p. 590
6.3.6.1
Rate switching along with internal sampling rate switching
p. 590
6.3.6.2
Rate switching along with coding mode switching
p. 590
6.3.6.3
Adaptive post-filter reset and smoothing
p. 590
6.3.7
Bandwidth switching
p. 590
6.3.7.1
Bandwidth switching detector
p. 590
6.3.7.2
Super wideband switching to wideband
p. 591
6.3.7.2.1
TBE mode
p. 591
6.3.7.2.2
Multi-mode FD BWE mode
p. 593
6.3.7.2.3
MDCT core
p. 594
6.3.7.3
Wideband switching to super wideband
p. 594
6.4
De-emphasis
p. 594
6.5
Resampling to the output sampling frequency
p. 594
6.6
Decoding of frame erasure concealment side information
p. 594
6.7
Decoding in DTX/CNG operation
p. 595
6.7.1
Overview
p. 595
6.7.2
Decoding for LP-CNG
p. 595
6.7.2.1
LP-CNG decoding Overview
p. 595
6.7.2.1.1
CNG parameter updates in active periods
p. 595
6.7.2.1.2
DTX-hangover based parameter analysis in LP-CNG mode
p. 596
6.7.2.1.3
LP-CNG low-band energy decoding
p. 598
6.7.2.1.4
LP-CNG low-band filter parameters decoding
p. 598
6.7.2.1.5
LP-CNG low-band excitation generation
p. 598
6.7.2.1.6
LP-CNG low-band synthesis
p. 600
6.7.2.1.7
LP-CNG high-band decoding and synthesis
p. 600
6.7.2.2
Memory update
p. 602
6.7.3
Decoding for FD-CNG
p. 602
6.7.3.1
Decoding SID frames in FD-CNG
p. 602
6.7.3.1.1
SID parameters decoding
p. 603
6.7.3.1.2
SID parameters interpolation
p. 603
6.7.3.1.3
LPC estimation from the interpolated SID parameters
p. 604
6.7.3.2
Noise tracking during active frames in FD-CNG
p. 604
6.7.3.2.1
Spectral partition energies
p. 604
6.7.3.2.2
FD-CNG noise estimation
p. 605
6.7.3.2.3
Noise shaping in FD-CNG
p. 605
6.7.3.3
Noise generation for SID or zero frames in FD-CNG
p. 607
6.7.3.3.1
Update of the noise levels for FD-CNG
p. 607
6.7.3.3.2
Comfort noise generation in the frequency domain
p. 607
6.7.3.3.3
Comfort noise generation in the time domain
p. 607
6.7.3.3.4
FD-CNG decoder memory update
p. 609
6.8
AMR-WB-interoperable modes
p. 610
6.8.1
Decoding and speech synthesis
p. 610
6.8.1.1
Excitation decoding
p. 610
6.8.1.2
Excitation post-processing
p. 611
6.8.1.2.1
Anti-sparseness processing
p. 611
6.8.1.2.2
Gain smoothing for noise enhancement
p. 611
6.8.1.2.3
Pitch enhancer
p. 611
6.8.1.3
Synthesis filtering
p. 611
6.8.1.4
Music and Unvoiced/inactive Post-processing
p. 611
6.8.1.4.1
Music post processing
p. 611
6.8.1.4.2
Unvoiced and inactive post processing
p. 612
6.8.1.5
Synthesis filtering and overwriting the current CELP synthesis
p. 615
6.8.1.6
Formant post-filter
p. 615
6.8.1.7
Comfort noise addition
p. 615
6.8.1.8
Bass post-filter
p. 615
6.8.2
Resampling
p. 616
6.8.3
High frequency band
p. 616
6.8.3.1
Preliminary estimation steps
p. 616
6.8.3.1.1
Estimation of tilt, figure of merit and voice factors
p. 617
6.8.3.1.2
Estimation of sub-frame gains based on LP spectral envelopes
p. 618
6.8.3.2
Generation of high-band excitation
p. 621
6.8.3.2.1
DCT
p. 621
6.8.3.2.2
High band generation
p. 621
6.8.3.2.3
Extraction of tonal and ambiance components
p. 623
6.8.3.2.4
Recombination
p. 624
6.8.3.2.5
Filtering in DCT domain
p. 625
6.8.3.2.6
Inverse DCT
p. 626
6.8.3.2.7
Gain computation and scaling of excitation
p. 626
6.8.3.3
LP filter for the high frequency band
p. 628
6.8.3.4
High band synthesis
p. 628
6.8.4
CNG decoding
p. 628
6.9
Common post-processing
p. 629
6.9.1
Comfort noise addition
p. 629
6.9.1.1
Noisy speech detection
p. 629
6.9.1.2
Noise estimation for CNA
p. 630
6.9.1.2.1
CNA noise estimation in DTX-on mode when FD-CNG is triggered
p. 630
6.9.1.2.2
CNA noise estimation in DTX-on mode when LP-CNG is triggered
p. 630
6.9.1.2.3
CNA noise estimation in DTX-off mode
p. 630
6.9.1.3
Noise generation in the FFT domain and addition in the time domain
p. 630
6.9.1.4
Noise generation and addition in the MDCT domain
p. 631
6.9.2
Long term prediction processing
p. 631
6.9.2.1
Decoding LTP parameters
p. 631
6.9.2.2
LTP post filtering
p. 632
6.9.3
Complex low delay filter bank synthesis
p. 634
6.9.4
High pass filtering
p. 635