Table of Contents

 1 Scope
 2 References
 3 Terms and definitions
        3.1 acoustic echo
        3.2 cancelled end
        3.3 combined loss (A_COM)
        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 (t_d)
       3.14 echo return loss (ERL) (A_ECHO)
       3.15 echo return loss enhancement (ERLE) (A_CANC)
       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 (A_NLP)
       3.23 open echo path
       3.24 pure delay (t_r)
       3.25 residual echo level (L_RES)
       3.26 returned echo level (L_RET)
       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 (T_SUP)
        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
Annex E – Embedded Echo Cancellers (EECs)
        E.1 Scope
        E.2 Definitions
        E.3 EEC requirements
      Page
        E.4 EEC testing
        E.5 Special considerations
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)
Appendix VIII – Test methodologies for use on embedded echo cancellers
     VIII.1 Introduction
     VIII.2 Test Methodology 1: Testing with the aid of a special "Test Mode" (under study)
     VIII.3 Test Methodology 2: Testing without access to control signals (under study)
Bibliography