Table of Contents

 1     Introduction and references             
        1.1     Introduction   
        1.2     References     
 2     Outline of LD-CELP 
        2.1     LD-CELP encoder          
        2.2     LD-CELP decoder          
 3     LD-CELP (encoder principles)             
        3.1     Input PCM format conversion
        3.2     Vector buffer
        3.3     Adapter for perceptual weighting filter              
        3.4     Perceptual weighting filter      
        3.5     Synthesis filter              
        3.6     VQ target vector computation               
        3.7     Backward synthesis filter adapter         
        3.8     Backward vector gain adapter
        3.9     Codebook search module        
       3.10     Simulated decoder    
       3.11     Synchronization and in-band signalling              
 4     LD-CELP decoder principles
        4.1     Excitation VQ codebook            
        4.2     Gain scaling unit           
        4.3     Synthesis filter              
        4.4     Backward vector gain adapter
        4.5     Backward synthesis filter adapter         
        4.6     Postfilter         
        4.7     Postfilter adapter        
        4.8     Output PCM format conversion            
 5     Computational details          
        5.1     Description of basic coder parameters               
        5.2     Description of internal variables            
        5.3     Input PCM format conversion (block 1)              
        5.4     Vector buffer (block 2)              
        5.5     Adapter for perceptual weighting filter (block 3, Figure 4-a)     
        5.6     Backward synthesis filter adapter (block 23, Figure 5)  
        5.7     Backward vector gain adapter  (block 20, Figure 6)        
        5.8     Perceptual weighting filter      
        5.9     Computation of zero-input response vector    
       5.10     VQ target vector computation              
       5.11     Codebook search module (block 24)  
       5.12     Simulated decoder (block 8)  
       5.13     Filter memory update for blocks 9 and 10        
       5.14     Decoder (Figure 3)     
Annex A – Hybrid window functions for various LPC analyses in LD-CELP    
        A.1     Hybrid window for the synthesis filter               
        A.2     Hybrid window for the log-gain predictor         
        A.3     Hybrid window for the perceptual weighting filter       
Annex B – Excitation shape and gain codebook tables    
Annex C – Values for bandwidth broadcasting    
Annex D – Coefficients of the 1 kHz lowpass elliptic filter used in  pitch period extraction module (block 82)    
Annex E – Time scheduling the sequence of computations    
Annex F – Alphabetical list of abbreviations used in this Recommendation    
Annex G – 16 kbit/s fixed point specification    
        G.1     Introduction  
        G.2     Algorithmic changes  
        G.3     Pseudo-code for other modules of ITU-T G.728            
        G.4     LD-CELP internal variable representations       
        G.5     Log-gain tables for gain and shape codebook vectors 
        G.6     Integer values of gain codebook related arrays             
        G.7     Encoder and decoder main program pseudo-codes    
Annex H – Variable bit rate LD-CELP operation mainly  for DCME at rates less than 16 kbit/s    
        H.1     Introduction  
        H.2     Principles of operation              
        H.3     Modifications for 12.8 kbit/s operation              
        H.4     Modifications for 9.6 kbit/s operation
Annex I – Frame or packet loss concealment for the LD-CELP decoder    
        I.1                   Scope   
        I.2                   Normative references  
        I.3                   Introduction      
        I.4                   Principles of operation 
        I.5                   Pseudo-code for frame erasure concealment    
        I.6                   Additional coder parameters and variables         
Annex J – Variable bit-rate operation of LD-CELP mainly for voiceband-data applications in DCME    
        J.1                   Scope   
        J.2                   Normative references  
        J.4                   Algorithm description   
Appendix I – Programs and test sequences for implementation verification of the algorithm of the ITU-T G.728 16 kbit/s LD-CELP speech coder    
        I.1                   General               
        I.2                   Test configurations        
        I.3                   Verification programs   
        I.4                   Test sequences               
        I.5                   Verification tools distribution    
Appendix II – Speech performance    
       II.1     Introduction   
       II.2     Speech performance  
       II.3     Performance with non-speech signals
       II.4     Artificial voice signals  
Appendix III – Values used for scaling ETPAST during frame erasures