Table of Contents

 1     Scope            
 2     References   
 3     Terms and definitions               
        3.1     acoustic echo    
        3.2     cancelled end    
        3.3     combined loss (ACOM)      
        3.4     comfort noise   
        3.5     composite echo
        3.6     convergence      
        3.7     convergence time             
        3.8     double-talk        
        3.9     echo canceller   
       3.10     echo cancellers in tandem            
       3.11     echo path         
       3.12     echo path capacity (∆)  
       3.13     echo path delay (td)        
       3.14     echo return loss (ERL) (AECHO)     
       3.15     echo return loss enhancement (ERLE) (ACANC)         
       3.16     electric echo     
       3.17     H register          
       3.18     H register reset 
       3.19     leak time          
       3.20     non-cancelled end          
       3.21     non-linear processor (NLP)           
       3.22     non-linear processing loss (ANLP)  
       3.23     open echo path               
       3.24     pure delay (tr)  
       3.25     residual echo level (LRES)               
       3.26     returned echo level (LRET)              
       3.27     signal processing device (SPD)     
       3.28     signal processing function (SPF)  
       3.29     signal processing network equipment/element (SPNE)           
 4     Abbreviations and acronyms  
 5     Test signals  
 6     Characteristics of echo cancellers           
        6.1     General              
        6.2     Purpose, operation and environment           
        6.3     External enabling/disabling           
        6.4     Tests and requirements for performance with input signals applied to the send and receive paths     
 7     Characteristics of an echo canceller tone disabler               
        7.1     General              
        7.2     Detector characteristics  
        7.3     Guardband characteristics             
        7.4     Holding-band characteristics         
        7.5     Operate time     
        7.6     False operation due to speech currents        
        7.7     False operation due to data signals              
        7.8     Release time     
        7.9     Other considerations       
 8     Non-linear processors (NLPs) for use in echo cancellers     
        8.1     Scope 
        8.2     General principles and guidelines  
Annex A – Description of an echo canceller reference tone disabler    
Annex B – Description of a reference non-linear processor    
        B.1     General              
        B.2     Suppression threshold (TSUP)         
        B.3     Static characteristics of activation control 
        B.4     Dynamic characteristics of activation control          
        B.5     Frequency limits of control paths
        B.6     Testing               
Annex C – Composite source signals for testing of speech echo cancellers – Signal, description and analysis    
        C.1     Introduction     
        C.2     Composite source signal – General considerations   
        C.3     Bandlimited composite source signal with speech like power density spectrum – Practical realization for measurements of echo cancellers    
        C.4     Appropriate analyses to determine convergence characteristics of speech echo cancellers using the composite source signal    
Annex D – Echo-path models for testing of speech echo cancellers    
        D.1     Introduction     
        D.2     Echo path models from network hybrid simulator   
        D.3     Echo path models measured from telephone networks in North America          
        D.4     Echo path models measured from telephone networks in Europe        
Appendix I – Guidance for application of echo cancellers    
        I.1     Scope  
        I.2     Echo control in the public switched telephone network            
        I.3     Application rules and operational constraints            
        I.4     Effect of cancellers on voice and data services         
        I.5     High-level speech             
        I.6     Network and service evolutionary considerations     
        I.7     Considerations regarding echo canceller performance during double talk            
Appendix II – Measurement methods for characteristics of echo paths    
       II.1     Introduction      
       II.2     Measurement procedure
       II.3     Analysis of echo-path characteristics          
       II.4     Examples of echo path measurements from real networks    
       II.5     Conclusions      
Appendix III – Multiple tail circuits    
Appendix IV – Guidelines on the use of parameters for testing echo cancellers    
Appendix V – List of low speed modems for optional use with Test No. 14    
Appendix VI – Example control interfaces    
       VI.1     Parallel Transistor-Transistor Logic (TTL) connection for digital signals            
       VI.2     Serial data link (ITU-T V.24 or RS-232) for software commands        
Appendix VII – Guidance on echo canceller orientation in conference bridge applications    
      VII.1     Introduction    
      VII.2     Echo canceller oriented towards the hybrid of the conference bridge participant (recommended)    
      VII.3     Echo canceller oriented away from the hybrid of the conference bridge participant (not recommended)