Overview

Acoustic echo is a common phenomenon that is encountered in many types of phone calls. It occurs when speaker output is fed back to the microphone input. This will disturb the far end speaker as they hear their own voice but delayed. Acoustic echo cancellers (AEC) are used in phones or in the network to minimize this distortion. Acoustic echo, unlike line echo, is dynamic during a call as people and speakers move about.

GL's Automated Acoustic Echo Cancellation (AEC) Compliance Test Software (PKB081) is a feature rich application used to perform acoustic echo cancellation testing in accordance with ITU-T Specifications, G.167 (03/1993) and P.340 (05/2000).

Screenshot of Automated Acoustic Echo Cancellation Test Software for E1

The Automated AEC Test Software uses GL Communications' T1 E1 Analyzer products and the customers AEC hardware or software to perform Acoustic Echo Canceller testing. Rin and Sin files (stimulus and echo) are prepared by Automated AEC Test software in accordance with user inputs. Rout and Sout are captured and processed.

---

Theory of operation

The module, which includes AEC, Rin, Rout, Sin and Sout, can be a Sound Card, a Mobile Phone, a Regular Phone, an IP Phone, or a Speaker Phone. Rin is the source signal (from the far end), which goes through Acoustic Echo Canceller (AEC) and Sout is the echo cancelled signal, which comes out of AEC. The leakage from Rout to Sin is due to the acoustic echo.

In the past, modeling and replicating acoustic echo has been quite complicated often requiring a sound chamber, head and torso, etc. GL has simplified the process considerably by modeling the acoustic echo path and dynamically changing its characteristics. In effect, the echo path can be made to vary in a manner similar to the real world. Also, the echo path can be specified to mimic a "small room", a "car", a "medium size conference room", etc. Dynamism is introduced by slowly morphing the impulse response coefficients in a predetermined manner.

The above features have been incorporated into DSP operators within our Windows Client Server (WCS) software. This software is available with our T1 E1 product platforms, including Dual PCIe Express cards and tProbe™ T1 E1 units. GL's T1 E1 Analyzer cards is featured with the Windows Client/Server DSP Operation module, which allows real-time testing using DSP commands to perform functions such as Amplification/Attenuation, Delay, Filter, File Tx/Rx, Logical operations, Echo Cancel, and so on.

Our DSP Operators in Windows Client Server (WCS) software offers following capabilities:

• Simulate acoustic echo into a mobile phone
• Generate dynamic (changing) acoustic echo
• Test acoustic echo cancellers in mobile phones and other signal processing devices

For comprehensive information, please visit Dynamic DSP Operation web page.

Automated Acoustic Echo Cancellation (AEC) test software works in conjunction with our T1 E1 product platforms, including Dual PCIe Express cards and tProbe™ T1 E1 units. Automated AEC Test Software performs a full analysis (with detailed displays) that results in a "Pass" or "Fail". Automated AEC testing concepts are implemented within the software for various End to End Applications (Mobile, TDM, and VoIP) scenarios.

---

Supported Test Cases - G.167, P.340 standards

Automated Acoustic Echo Canceller (AEC) Test software is designed to test AEC conformance as per the ITU-T Specifications, G.167 (03/1993), and P.340 (05/2000). Following test cases are currently supported:

Test Cases	Description	G.167	P.340
TCLwst	Weighted terminal coupling loss - single talk	Yes	Yes
TCLwdt	Weighted terminal coupling loss - double talk	Yes	Yes
Ardt	Received speech attenuation during double talk	Yes	Yes
Asdt	Sent speech attenuation during double talk	No	No
Drdt	Received speech distortion during double talk	No	No
Dsdt	Sent speech distortion during double talk	No	No
Pr	Maximum frequency shift (or pitch ratio)	No	No
Tonst	Break-in time - simple talk	No	No
Tondt	Break-in time - double talk	No	No
Tic	Initial convergence time	No	No
Trdt	Recovery time after double talk	No	No
TCLwpv	Terminal coupling loss during echo path variation	No	No
Trpv	Recovery time after echo path variation	No	No

---

Features

• Simulates an actual acoustic echo path with acoustic filter types (Small, Medium, Large Office), Echo path delays and losses
• Features such as filter, attenuate, and delay are available as well as slow filter coefficient variation as a function of time to simulate a real acoustic environment
• Real-time as well as off-line analysis with tabular Pass/Fail results
• Simulate acoustic echo for Analog (Mobile Phone), digital (Gateway), and Packet (VoIP IP Phone) applications
• Auto or Manual control of the AEC during testing
• Auto analysis of the response according to G.167 (03/1993) & P.340 (05/2000) requirements
• Detailed graphical and tabular results for individual and overall test
• Generation of report with the plots (Report Analysis)
• Options to recalculate test parameter across different region in the waveform (Plot Results)
• Option to zoom-in on any test results to investigate further
• Supported on Windows Operating System with user-friendly Graphical User Interface
• Compatible with GL's tProbe™ T1 E1 units and Dual PCIe Express cards

---

AEC Testing Scenarios

• Scenario 1 - Stimulus / Simulation all Digital (TDM Applications)

In this scenario, the AEC is assumed to be located in the network. Acoustic echoes are simulated within the GL's T1 E1 platforms digitally. The generation of the stimulus signal and the capture of the response signal is also performed by GL's T1 E1 platforms.


Stimulus & Simulation Digital (TDM)


• Scenario 2 - Stimulus / Simulation all Analog (Mobile Phone Applications)

In this scenario, the AEC is assumed to be in a mobile phone and accessed thru an analog interface. Again GL's T1 E1 platforms with analog interfaces are used to convert analog signals to digital and subsequent processing is performed digitally. Level adjustment accessories are used between mobile phone and the Dual PCIe Express cards to accommodate various signal levels and impedances.




Stimulus & Simulation Analog using Single Timeslot (8 bit)

Screenshot of Stimulus & Simulation Analog using Two Timeslots (16 bit)

Auto AEC Software - Echo Simulation & Monitoring



• Scenario 3 - Stimulus RTP (Ethernet) / Simulation Analog or Digital (VoIP IP Phone Applications):

In this scenario, the stimulus and response signals are generated by GL's RTP Toolbox™ through an Ethernet interface and simulation is performed digitally by GL's T1 E1 platforms, whether accessed through analog or digital interfaces.


Stimulus RTP (Ethernet) - Simulation Digital using Single Timeslot (8 bit)

Screenshot of Stimulus RTP (Ethernet) - Simulation Digital using Two Timeslots (16 bit)




Stimulus RTP (Ethernet) - Simulation Analog using Single Timeslot (8 bit)

Screenshot of Stimulus RTP (Ethernet) - Simulation Analog using Two Timeslots (16 bit)

---

Setting up Test parameters per G.167 in AEC Test Software

---

AEC Test Software Results

Report Analysis

Auto AEC Test performs a full analysis (with detailed displays) that results in a "Pass" or "Fail". Supports *.csv and *.xls format files for reporting AEC Test results analysis.

The graphs below depict the result analysis per G.167. For the 'Pass' cases, both the convergence time and the residual should meet the requirements of G.167.

For the 'Fail' cases, either one (convergence or residual) or both (convergence and residual) does not meet the requirements of G.167.

Screenshot of AEC Test Software Results

Plot Results

Plot Result option enables to recalculate test parameter across different regions in the waveform.

The plot result displays Rin, Sout files and part of the Rin and Sout files used to calculate the test parameter.

Red background color indicates test fail and green indicates test pass. The part of the file used for calculation is also displayed in seconds. The user can recalculate the test parameter providing necessary valid information as shown below.

Users can change the recalculate options, the current start point of calculation of the test parameter and length used for it.

Screenshot of AEC Test Software Plot Results

---

Resources

Please Note: The XX in the Item No. refers to the hardware platform, listed at the bottom of the Buyer's Guide, which the software will be running on. Therefore, XX can either be ETA or EEA (Octal/Quad Boards), PTA or PEA (tProbe Units), XUT or XUE (Dual PCIe Express) depending upon the hardware.

 Back to Echo Canceller Testing Solutions Main Page