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Echo Cancellation in VoIP Systems

Updated on May 1, 2012
VoIP Echo Cancellation
VoIP Echo Cancellation

Echo Problems with VoIP

The problem of the person hearing what they just said come back to them a few dozen milliseconds later is more common than you think. You may not realize it but every telephone call is susceptible to echo and it's only because the PSTN system has had decades to perfect its standards and infrastructure that we don't experience any of it today. Even so, many of us have been exposed to echo on a telephone call now and then. Local PSTN calls don't struggle with this as much because the delay is too low and for an echo on a phone call to be noticeable it has to be both loud and delayed sufficiently long for our ears to be able to tell the difference. Strictly speaking when we talk, our conversation is being transmitted to us through two different mediums – via the air and via the bone. The latter travels much faster than the former and this is why our voices sound different to us compared to how they sound to other people.

VoIP faces a problem with echo that is more serious than the one with the PSTN system because the latency is greater. As the IP packet travels to various routers, it picks up a few milliseconds each time and that contributes to the higher perception of echo.

VoIP Echo Cancellation

Given the fact that a certain amount of echo is inevitable in a communication system based on audio combined with the tendency of VoIP for higher latency, how does one go about reducing or removing the impact created by it? There are several ways to do this and VoIP phones generally make use of an echo cancellation algorithm. Fortunately because VoIP is an Internet-based IP application, we can use software to implement it instead of expensive hardware devices of the kind that is necessary to work with the PSTN network.

An echo cancellation algorithm tries to extract the vestiges of the original signal from the one that comes back. For this, it has to measure the delay as well as the attenuation of the echo. The attenuation determines to what extent the echo has diminished in volume on its way back. Armed with these two pieces of information, we can design a mathematical algorithm to subtract the remnants of the original signal from the returning one thereby nullifying its effects and delivering the pure signal that is transmitted from the person at the other end.

There are many ways to implement the various VoIP echo cancellation algorithms. Depending on the complexity of your SIP client, you may need to set one of many parameters to fine-tune the echo cancellation settings. Your VoIP business phone service should be able to give you the appropriate recommendations that work properly with their product. It might vary between the different business VoIP services available. Click here to find out more.


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      nurtim 5 years ago

      I agree, that echo cancellation is a big issue with VoIP. As you said, for VoIP we should use software for echo cancellation instead of hardware. I think one of the leading companies in the area of software echo cancellation for VoIP is SoliCall.