CONTENTS

�1���� Scope
�2���� References
�3���� Terms and definitions
�4���� Abbreviations
�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
����������������� 6.4.1���� Transmission performance
����������������� 6.4.2���� Echo canceller performance
�7���� Characteristics of an echo canceller tone disabler
������� 7.1���� General
������� 7.2���� Detector characteristics
����������������� 7.2.1���� Phase reversal detection
������� 7.3���� Guardband characteristics
����������������� 7.3.1���� Noise tolerance
������� 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���� NLPs for use in echo cancellers
������� 8.1���� Scope
������� 8.2���� General principles and guidelines
����������������� 8.2.1���� Function
����������������� 8.2.2���� Suppression threshold
����������������� 8.2.3���� Control of NLP activation
����������������� 8.2.4���� Frequency limits of control paths
����������������� 8.2.5���� Signal attenuation below threshold level
����������������� 8.2.6���� Testing of NLPs
Annex A � Description of an echo canceller reference tone disabler
Annex B � Description of a Reference NLP
������� 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.2.1���� General description of the different sequences
����������������� C.2.2���� Calculation and analysis using a composite source signal
������� C.3���� Bandlimited Composite Source Signal with speech like power density spectrum � practical realization for measurements of echo cancellers
����������������� C.3.1���� Composite Source Signal for single talk
����������������� C.3.2���� Bandlimited Composite Source Signal to simulate double talk
������� C.4���� Appropriate analyses to determine convergence characteristics of speech echo cancellers using the Composite Source Signal
����������������� C.4.1���� Calculation in the frequency domain
����������������� C.4.2���� Calculation in the time domain
����������������� C.4.3���� Level calculations according to the active speech level P.56
Annex D � Echo-path models for testing of speech echo cancellers
������� D.1���� Introduction
����������������� D.1.1���� CSS or white noise input
����������������� D.1.2���� Tone(s) input
������� 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 PSTN
����������������� I.2.1���� Echo suppressors
����������������� I.2.2���� Echo cancellers
����������������� I.2.3���� Responsibilities of modem manufacturers and end users
������� I.3���� �� Application rules and operational constraints
������� I.4���� �� Effect of cancellers on voice and data services
������� I.5���� �� High-level speech
����������������� I.5.1���� Introduction
����������������� I.5.2���� Double talk detection and activity detection
����������������� I.5.3���� Effects of low bit rate coders
����������������� I.5.4���� Effects of a non-linear echo path
����������������� I.5.5���� Guidelines for Rout usage in echo cancellers
������� I.6���� �� Network and service evolutionary considerations
����������������� I.6.1���� Bit transparency of echo cancellers
����������������� I.6.2���� Convergence speed
����������������� I.6.3���� Acoustic echo control and environments
����������������� I.6.4���� Comfort Noise
������� I.7���� �� Considerations regarding echo canceller performance during double talk
����������������� I.7.1���� Introduction
����������������� I.7.2���� Double talk parameters
����������������� I.7.3���� Analysis of technical parameters that influences performance under double talk conditions
����������������� I.7.4���� Conducting the double talk Tests 3A and 3B without inhibiting the adaptation
����������������� I.7.5���� Subjective and objective echo canceller testing
������� I.8���� �� Guidelines on the use of parameters for testing echo cancellers
������� I.9���� �� Bibliography
Appendix II � Measurement methods for characteristics of echo paths
������ II.1���� Introduction
������ II.2���� Measurement procedure
���������������� II.2.1���� Measurement set-up
���������������� II.2.2���� Computation of the echo path impulse response
������ II.3���� Analysis of echo-path characteristics
���������������� II.3.1���� Dispersion time
���������������� II.3.2���� Magnitude response of echo path
������ II.4���� Examples of echo path measurements from real networks
���������������� II.4.1���� Echo-path characteristics from measurements in North America
���������������� II.4.2���� Echo path characteristics from measurements in Europe
������ II.5���� Conclusions
������ II.6���� Bibliography
Appendix III � Multiple tail circuits