Echo Cancellation Research Paper

944 Words4 Pages

K.V.Mohana Prasath [1], Dr.N.Kasturi [2]
[1 ]PG Scholar, school of communication and Computer sciences, [2]Professor,school of communication and Computer sciences
Department of Electronics and Communication Engineering ,
Kongu Engineering College, Perundurai-638052 ,

Abstract - Acoustic echo cancellation is a common occurrence in today’s telecommunication systems. Currently, echo cancellation is a most interesting and challenging task in any communication system. Echo is a delayed and degraded version of original signal that travels back to its source after several reflections. Eliminating this effect without affecting the original quality
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Echo cancellation is one of the most widely used digital signal processing devices in the world because each telephone call requires a pair of echo cancellers. Echo cancellation is an essential signal enhancement tool in hands-free communication. Acoustic echo is caused due to leakage from the loudspeaker to the microphone in settings like hands free telephony. Basically, a transversal filter, which is adaptively modeling the echo path impulse responses, generates an estimate of the echo, with this an echo estimate is created at the right time to cancel the actual echo. The common problems faced by echo cancellation are the convergence time and the degree of cancellation. Convergence time is the time taken to reach an acceptable level of steady state residual echo. Degree of cancellation is the amount of echo cancelled, measured in Echo Return loss Enhancement. In Adaptive acoustic echo cancellation , the convergence time is high and due to the large number of multiplications it is rather costly to be
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The building blocks are
1) Echo generator
2) Difference amplifier
3) Phase shifter
4) Sound processor UPC 1892

A) Echo Generator

The input signal of echo generator is acquired from the microphone. The echo generator block generates echo by means of Phase shifters in the given input signal along with delay

B) Phase Shifter

A phase shifter is microwave network which provides a controllable phase shift of input signal. It provides invariable phase shift with frequency. Phase shifters of angle 90,180,270 and 360 .


The difference amplifier with LM3 amplifies the difference between two voltages making this type of operational amplifier circuit , a subtractor. The phase shifted output is fed to both difference amplifier and phase shifter. The phase shifter cancels the echo in the signal.The difference amplifier subtracts the input signal with echo and echo cancelled output of phase shifter. The output of difference amplifier is signal with 80% of echo being removed.


It is a specific IC to reproduce surround sound by using phase shifters and a signal matrix. Inorder to enhance the signal ,the output of difference amplifier is fed to sound processor to enchance it to 100 % . The output is amplified and fed to the

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