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