Acoustic Echo Cancellation

What is Acoustic Echo, and Why Does It Occur?

Let's explore the concept of Acoustic Echo and its causes. This phenomenon typically arises based on the sound capture methods used by communication devices during calls.

When using a speakerphone, the person on the other end is heard through your device's loudspeaker, which is what we call "far-end speech." Simultaneously, your voice is picked up by your device’s microphone and transmitted across to the other participant, known as "near-end speech."

Unfortunately, microphones are not selective and may capture both near-end and far-end speech. If the far-end speech is picked up and sent back to the originating party, they will experience their own words echoing back at them after a short interval caused by network transmission and processing times.

This echo is more common when using a device’s speakerphone function, and one workaround is to switch to using headphones. Nonetheless, even mobile or other telephone devices can have this issue due to the physical design where earpiece speakers and microphones are close enough to enable their interaction.

The concern here is with the “echo,” and its disruptiveness depends on the duration of the delay. There's a certain threshold where the length of an echo turns from being barely noticeable to significantly hampering the conversation.

Distinguishing Acoustic Echo from Room Echo

When people think of an "echo," they often envision the experience of their voice bouncing back at them in a large, empty space—this is known as room echo and is quite distinct from the acoustic echo encountered during a call or virtual meeting.

The Impact of Echo on Calls

It might seem that a small amount of echo wouldn't be much of a disturbance during a call, but even minimal echo can disrupt one's ability to listen effectively. Echoes that have a delay shorter than 40 milliseconds (ms) tend to go unnoticed and typically don't bother the listener. However, when the delay exceeds 40ms, it becomes detectable to the human ear. An echo delay of this magnitude can make conversations difficult to comprehend. Throughout an entire phone call, such an echo can greatly irritate all parties involved. Moreover, it can lead to misunderstandings and missing crucial information during the conversation.

How Does Acoustic Echo Cancellation Work?

To eliminate Acoustic Echo, let’s delve into the solution offered by Acoustic Echo Cancellation (AEC) technology.

The essence of AEC lies in its ability to prevent the far-end speech from being retransmitted back to the caller. It aims to exclude echoes, ambient reverberations, and any extraneous noises within the acoustic environment from the outgoing audio signal.

AEC operates through a dynamic filtering process. It utilizes an adaptive algorithm to tailor a filter that models and tracks the acoustic path. The filter then suppresses the reflected sound from the signal pathway, ensuring that the outgoing audio is echo-free.

For example, imagine you're on a call using a speakerphone. An AEC filter would isolate and inhibit any echo or room noise from your environment, ensuring that only your voice reaches the other party.

Moreover, this intelligent filter distinguishes between incidental sounds within the acoustic environment and the intended speech. For instance, if music plays in the background, the filter can identify and neutralize the music picked up by the microphone, resulting in crisp communication.

Consider a hands-free call in your car with the stereo on—the AEC would allow you to continue enjoying the music without interrupting your conversation. It focuses on canceling out both the music and the other party’s voice from the microphone's reception, ensuring that the person on the far end hears only the local speaker.