What is Echo in VoIP and the Importance of Echo Cancellation for Audio Clarity

Echo Cancellation

Audio clarity is taken for granted by users of 4G LTE and VoIP. However, it was not always so. In the early days of VoIP one big stumbling block to wider adoption was loss of audio clarity, delays, breaks and echo. Echo voice can be particularly disturbing since it interferes with conversations carried out over VoIP. The problem is largely resolved by the use of sophisticated echo cancellation software.

Musicians and recording industry actually introduce echo as a desirable special effect but it is strictly No-No for business talks where you do not want your own voice drowning out what the person at the other end is saying.

What causes echo in VoIP

Echo becomes noticeable and distracting when there is a delay of over 50 milliseconds in the caller’s voice in the outgoing microphone being reflected back in the incoming audio stream. Echo becomes a problem when it is loud and there is a delay between the originating signal and the bounced back signal. This can happen due to various reasons:

    • The caller’s voice goes to the recipient’s handset’s speaker and, from there, it is picked up by the microphone and transmitted back resulting in acoustic echo.
    • Signals travel over wires and can be picked up by receiving wire leading to line echo.
    • Poorly designed and implemented cabling, damaged or wet cables and bridge taps or due to cheap quality phones.
    • Voice signal travels a lengthy route through internet and through satellite links which can introduce latency across network hops. The result is echo.
    • Imbalanced PSTN-VoIP hybrid wiring causing reflections being passed back to the caller through the VoIP link.
    • Echo voice can be problematic when you use hands-free phone, use your handset in speakerphone mode and use external bluetooth connected speakers.
    • Electromagnetic interference from other devices could also cause echo voice.
    • In VoIP in particular, echo happens due to delay caused by compression-decompression time and use of specific VoIP Codec that samples voice data. Add to this delays in voice packet transmission and you have echo as the result.

As VoIP telephony grew it led to development of advanced echo suppression and echo cancellation technologies. Today, you can call any party anywhere in the world using your softphones and never worry about latency or echo.

Echo suppression and echo cancellation

The two methods achieve the same goal but by using different methods. Echo suppression works by detection of voice signal in one direction and muting it should it reverse direction of travel. The circuit usually is employed at the far end.

Echo cancellation is somewhat more sophisticated. It recognizes the original signal and its reappearance on the line with the associated delay. It then subtracts or removes that signal component from the transmitted or received signal. This technology can be built into a DSP chip or as is more common, implemented through algorithm based software. Should you be switching over to VoIP and if echo voice is one thing holding you back then you can be reassured by the fact that most VoIP developers offering IP PBX or WebRTC or call center software usually incorporate echo cancellation algorithms incorporating techniques such as measurement of echo return loss.

Typical echo cancellation in VoIP

Today’s advanced VoIP codecs usually incorporate echo cancellation technology. One typical algorithm works this way:

    • Generate multiple copies of received signal with progressive delays between each copy
    • Algorithm distinguishes when the actual delay syncs with self-generated delay
    • It then reduces the volume of the echo voice.

However, the way codecs implement it can differ. For instance, aggressive echo cancellation can equally hamper audio clarity by delivering choppy sound.

Managing echo voice

VoIP in itself does not cause echo directly since signals are digital packets. Extraneous factors, as stated above, are more responsible. Since echo is a function of the far end, even if you have top of the line IP PBX at your end, it will cause a problem. The echo cancellation technology must be in place at the far end too but usually engineers implement echo minimization at gateways. Efforts can lead to reduced delays which partly resolve echo voice issues.

The other factor is loudness measured in decibels. If echo strength exceeds a certain dB level it can cause annoyance. Typically, echo cancellation can suppress echo 6dB quieter than speech volume in the call. If it is the same volume or even higher volume then echo cancellation could disrupt both the echo and the natural audio stream. Loudness and delays are connected and echo return loss is an important metric. The longer the delay the higher the attenuation of the echo return signal needs to be, somewhere around 15 dB or even as much as 55 dB.

This is between two end points. There is another metric known as the ECOM value which measures the echo from the IP side. ITU G.168 defines ACOM as the combined echo return loss through the system or reduction of echo through any channels.

Another factor to consider is the physical set up of your phones, the type of hardware in use and the environment as well as local wiring. Resolving issues that could lead to echo voice could resolve the problem to a great extent and let the echo cancellation algorithm better do its job, assuming of course that the enterprise at the other end employs similar techniques and software. Signal in and signal out metrics can be set up to test circuits to check if echo is injected at the point of origin and then resolve it. Signal out measures signal from the IP network to the PSTN for amount of echo and uses software for resolution through attenuation/cancellation.

Your hardware, software and existing environment all contribute to echo (or absence of it). Following best practices is important, especially when you hold audio conferences for which it is a good idea to use microphone close to the mouth in an environment with some measure of audio damping to attenuate reflections. Software for VoIP is also important since some systems can incorporate monitoring and echo cancellation technology.

Echo becomes a problem when it is delayed and loud but you can cancel it and also use mitigating techniques to enjoy crystal clear audio.

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