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 echo canceller:
3.9 echo path:
3.10 echo path capacity (Δ):
3.11 echo path delay (td):
3.12 echo return loss (ERL) (AECHO):
3.13 echo return loss enhancement
(ERLE) (ACANC):
3.14 electric echo:
3.15 H register:
3.16 leak time:
3.17 non-cancelled end:
3.18 nonlinear processor (NLP):
3.19 nonlinear processing loss (ANLP
):
3.20 pure delay (tr):
3.21 residual echo level (LRES):
3.22 returned echo level (LRET):
3.23 open echo path:
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
6.4.3 Nonlinear echo 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 NLP's 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 NLP's
Annex A -
Description of an echo canceller reference tone disabler
A.1 General
A.2 Disabler characteristics
A.2.1 Tone detection
A.2.2 Phase reversal detection
A.3 Guardband characteristics
A.4 Holding-band characteristics
A.5 Operate time
A.6 False operation due to speech
currents
A.7 False operation due to data
signals
A.8 Release timeAnnex 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.2 Echo-Path Models from Network
Hybrid Simulator
D.3 Echo-path models measured from
telephone networks in North America
Appendix I - Guidance
for application of echo cancellers
I.1 Scope
I.2 Echo control in the PSTN
I.2.1 PSTN Transmission Planning
I.2.2 Echo Suppressors
I.2.3 Echo Cancellers
I.2.4 Responsibilities of Modem Manufacturers and End Users
I.3 Application Rules and Operational
Constraints
I.3.1 Public Network Transmission Planning
I.3.2 Delay Considerations
I.3.3 Provisioning of the Echo Path
Capacity and Echo Path characteristics
I.3.4 End User/Manufacturer/Private Network Transmission Planning
I.4 Effect of Cancellers on Voice and
Data services
I.4.1 Interaction with Voice-band Data
I.4.2 Interaction of Echo Control with Facsimile Transmission
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 Non-Linearities and time variant Effects in the Echo path
I.6.3 Voice Compression Between Tandem Cancellers
I.6.4 Tandeming of Echo Cancellers
I.6.5 Convergence Speed
I.6.6 Acoustic Echo Control and Environments
I.6.7 New Circuit Switched Service
I.6.8 Comfort Noise
I.7 Special DCME/PCME Networking Considerations
I.7.1 Detailed Interaction
I.7.2 Possible Solutions
I.8 Considerations regarding echo
canceller performance during double talk
I.8.1 Introduction
I.8.2 Double talk parameters
I.8.3 Analysis of Technical Parameters that Influences Performance Under
Double Talk Conditions
I.8.4 Conducting the Double Talk Tests 3A and 3B Without Inhibiting the
Adaptation
I.8.5 Subjective and Objective Echo Canceller Testing
I.9 Guidelines on the use of
parameters for testing echo cancellers
Appendix II -
Measurement Methods for Characteristics of Echo Paths and an example for the North American Network
II.1 Introduction
II.2 Measurement Procedure
II.3 Test Signal
II.4 Computation of Impulse Response
II.5 Analysis of Echo-Path
Characteristics
II.5.1 Dispersion Time
II.5.2 Magnitude Response of Echo Path
II.5.3 Echo-Path Characteristics from Measurements in North America
II.6 Conclusions
Appendix III - Multiple Tail Circuits
ITU-T Recommendation G.168