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
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
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 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.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 PSTN
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
I.8
Bibliography
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
II.6 Bibliography
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
TTL connection for digital signals
VI.2
Serial
data link (V.24 or RS-232) for software commands