Intro to Acoustic Echo Canceler

Let’s talk about Acoustic Echo Cancellation, or AEC,

and the way that you can incorporate it into your Q-SYS design.

At its simplest, AEC is a process applied to the audio of a telephone call

that prevents the talkers from hearing the echo of their own voice.

In AEC jargon there are two locations – the Near-End and the Far-End.

The Near-End is typically a conference room with integrated loudspeakers in the ceiling

or the table, and at least one microphone.

The Far-End is the remote caller, maybe in their hotel room, or their car, etcetera.

"Hello, can you hear me?"

The problem with this phone call is that the Far-End caller’s voice is broadcast from the loudspeakers

in the Near-End room, where it goes directly back into the microphone and is transmitted back to the Far-End.

"Can you hear me?"

In addition, this direct path is only one of many ways the voice can re-enter the microphone.

It could bounce off of the walls, off of the people in your room, it could bounce off of one wall,

against a bottle of water, back against a wall, against the back of your head, against the ceiling and down again

these are known as acoustic reflections, or echoes. Since these acoustic paths have different physical lengths,

they result in different time delays from the loudspeaker to the microphone.

And as the sound travels through the air and bounces of various surfaces,

it becomes distorted as different frequencies are absorbed and attenuated.

And all of this is sent back to the far end.

The average latency of telephone audio is about 50 ms, which means that as the Far-End talker speaks,

he’ll hear all these reflections of his own voice returned to him 100 ms later...

Are you hearing this echo? Because I’m having a lot of trouble understanding what you’re saying.

...which is guaranteed to make anyone tongue-tied...

My side is really echoey...

A natural solution to this problem would be to simply turn down the volume

on the return signal while the Far-End is talking,

but the problem with that is that the everyone in the Near-End room has to wait until the Far-End talker is done.

Try having a productive business meeting with walkie-talkies and you’ll see that one-at-a-time

communication isn’t a good option. So this is where the AEC system comes in.

AEC eliminates the return echo while preserving the sound of the Near-End talkers.

This may sound like a simple thing, and it’s easy to take it for granted.

Most people use it all the time without realizing it – when you use a speakerphone on your home telephone,

or Skype with a PC Speaker you’re using AEC devices.

You don’t notice what’s happening because, well, that’s the point. But take it away and you’ll notice it then.

So how does AEC work? For most people, a good answer would be: Magic.

Just be happy that it works and go about your business. For you, you want more answers.

In the next section we’ll take a look inside the AEC component at all the various sub-systems

that comprise this complete speech enhancement system.