What Is Acoustic Echo Cancellation and How Does It Work?


It’s a problem nearly everyone has experienced: you’re in the middle of a call, and suddenly everything you say is echoing back to you over the phone. Now it’s hard to concentrate or even get out a complete sentence without being interrupted by yourself. This issue is known as acoustic echo, but why does it happen? And, more importantly, what can be done to prevent it?

What is Acoustic Echo?

Acoustic echo refers to the same phenomenon that occurs when someone yells in a cave or talks in a large, empty room. In the cave or empty room, the actual sound waves are bouncing off of physical barriers. So, how does something echo during a phone call when the audio is entirely digital?
It happens when your voice is sent through the outgoing stream, only to be picked up by a microphone on the other end and reflected back via the incoming stream. In simpler terms, imagine someone talking into their cell phone. Their voice transmits to the person they’re talking to, but the microphone of the receiver picks up the words that were said and sends it back to the person speaking.
Depending on the echo interval, this can cause anything from a slight annoyance to a significant breakdown in communication. Usually, if the delay is 25 milliseconds or less, most people won’t even realize it. If the reverb reaches 55 milliseconds, it can sound like two people are saying the same thing at the same time. This echo is noticeable, but usually doesn’t significantly affect the user’s ability to communicate efficiently. Once the delay goes above 55 milliseconds, the echo interrupts the speaker, making it nearly impossible for them to keep their words straight. Having a conversation at this point is extremely difficult and, more often than not, leads to both parties prematurely ending the call.

Causes of Acoustic Echo

The leading cause of acoustic echo are speakerphones, which is why the issue is so prevalent during conference calls. This seems fairly obvious since when a voice comes out of a speakerphone, it’s also clearly picked up by the microphone. Overly sensitive microphones, speaker volume set too high, and receivers that are too close to one of the speakers amplify these issues.

How Acoustic Echo Cancellation Works

Echo can be reduced by adding sound absorbing materials like rugs and carpets, or through more undisguised means like acoustic panels. A more modern way to reduce echo, however, is by investing in equipment technology that does the work for you.
Acoustic echo cancellation (AEC) technology is a common addition to today’s conference phones. The technology recognizes and eliminates the echo as quickly as possible without affecting the audio quality. This concept may sound simple, but the actual process is challenging to achieve since you must take into account several factors. For example, the cancellation should continue to work even in situations where both sides of the conversation are talking at once or when there’s an abundance of background noise.
This technology works by utilizing a digital signal processing, or DSP, engine that thoroughly examines an incoming voice, while at the same time evaluating the outgoing stream. If it determines there is a copy of one voice in both streams, it removes the duplicate audio before sending it back to the original speaker. In doing so, the engine isolates the echo alone without removing a noticeable amount of other voices or noises, and without sacrificing the overall quality of the audio.
Another solution, albeit a simpler one, is a method known as half duplex or acoustic suppression. Essentially functioning as a walkie-talkie, a half-duplex system enables users to press down on a button when they want to speak. For as long as you press this button, all audio channels are muted except the one holding the button. This enables the user to speak uninterrupted for as long as they need and, due to the cancellation of all incoming channels, it removes the possibility of any feedback or acoustic echo.
The simplicity of audio suppression technology is also its biggest downfall, as it doesn’t allow for double-talk and can often disrupt the natural flow of conversations. One person speaking at a time can work for straightforward phone calls but can be a hindrance for phone calls that are meant to be more collaborative.
Learn more about acoustic echo cancellation and our suite of  products featuring this technology by contacting us today.

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