This page covers echo canceller basics and provide link to manufacturers of echo canceller.
Echo is the reflected copy of the original voice with some delay. This delayed copy of the original voice mixies with the ongoing conversation and it will be annoying. Another reason of the echo is reflected copy of the tone used for internet which will also cause problem in ongoing conversation.
Echo canceller uses advanced DSP techniques to reduce/eliminate the echo. It is placed in the 4 wire portion of the circuit. It stores estimate of the echo and substrate the same from the realtime echo to reduce/elimate its effect. It operates on 64 kbps line which in tern make primary 2mbps link or other rates. In the VSAT network it is connected in the 2Mbps link between MUX/DEMUX and modem. In the GSM network it is connected between MSC and TDM network.
General Echo canceller specifications are outlined below:
Echo Return Loss Enhancement or ERLE- It is attenuation of echo signal when it passes through send path of the echo canceller.
Echo Return Loss or ERL-It is ttenuation of a signal from Rout port to Sin port due to transmission & hybrid loss (tail path loss)
Tail Circuit Delay
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 Impedence- 75 Ohm or 120 Ohm
Echo Canceller Test/Evaluation Parameters
Input jitter tolerance
Output jitter tolerance in the absense of input jitter
Echo Return Loss (ERL)
Echo Return Loss Enhancement (ERL)
Tone disabler for Data Transmission
Tone disabler for in-band signalling
- 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
OCTASIC INC. - www.octasic.com
acoustic echo cancellation software from SoliCall-www.solicall.com
ITU-T Rec. G168, Reference 13