Echo Canceller Basics: Definition, Specifications, and Applications

This page covers echo canceller basics and provides links to manufacturers of echo cancellers. Echo is the reflected copy of the original voice with some delay. This delayed copy of the original voice mixes with the ongoing conversation and it will be annoying.

Another reason for the echo is the reflected copy of the tone used for the internet which will also cause a problem in the ongoing conversation. Echo cancellers use advanced DSP techniques to reduce/eliminate the echo. It is placed in the 4-wire portion of the circuit.

It stores an estimate of the echo and subtracts the same from the real-time echo to reduce/eliminate its effect. It operates on a 64 kbps line which in turn makes a primary 2mbps link or other rates.

In the VSAT network, it is connected in the 2Mbps link between MUX/DEMUX and the modem. In the GSM network, it is connected between the MSC and the TDM network.

Technical Specifications

General Echo canceller specifications are outlined below:

• Echo Return Loss Enhancement or ERLE: It is the attenuation of the echo signal when it passes through the send path of the echo canceller.
• Echo Return Loss or ERL: It is the attenuation of a signal from the Rout port to the Sin port due to transmission & hybrid loss (tail path loss).
• Convergence Time
• Tail Circuit Delay
• Tone Disablers
• Signaling Protocols: CAS, CCS etc.
• Framing format: Per ITU-T G.704:FAS, FAS +CRC4, CAS or CAS+CRC4
• Line rate - 2.048Mbps or any other rate
• Line Encoding - ITU-T G.703, G.704
• PCM Encoding - ITU G.711
• Jitter tolerance - ITU-T G.704, G.824
• Line Impedance - 75 Ohm or 120 Ohm

Echo Canceller Test/Evaluation Parameters

• Input jitter tolerance
• Output jitter tolerance in the absence of input jitter
• Echo Return Loss (ERL)
• Echo Return Loss Enhancement (ERL)
• Tone disabler for Data Transmission
• Tone disabler for in-band signaling

Applications

• Satellite-based VSAT Earth station
• GSM, CDMA, and other cellular technologies

Echo Canceller Manufacturers

• Ditech Networks - www.ditechnetworks.com
• GL Communications - www.gl.com
• Echo Cancellation Software from Vocal - www.vocal.com
• Cisco - www.cisco.com
• OCTASIC INC. - www.octasic.com
• acoustic echo cancellation software from SoliCall - www.solicall.com

References

• ITU-T Rec. G168, Reference 13

Echo Canceller Test Procedure and Test Equipments

This page describes the Echo Canceller Test Procedure. It mentions Echo Cancellation Test Equipments.

An echo canceller is the equipment used for echo cancellation. The echo canceller measurements performed by this test procedure include return loss, line rate, jitter, ERLE, continuity, tone disabler (data transmission, in-band signaling) etc.