Video Transcript
Intro to Acoustic Echo Canceler
2m 55s
0:08
Let’s talk about Acoustic Echo Cancellation, or AEC,
0:12
and the way that you can incorporate it into your Q-SYS design.
0:15
At its simplest, AEC is a process applied to a telephone calll
0:19
that prevents the talkers from hearing the echo of their own voices.
0:22
In AEC jargon there are two locations – the Near-End and the Far-End.
0:28
The Near-End is typically a conference room with integrated loudspeakers in the ceiling
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or the table, and at least one microphone.
0:34
The Far-End is the remote caller, maybe in their hotel room, or their car, etcetera.
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"Hello, can you hear me?"
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The problem with this phone call is that the Far-End caller’s voice is broadcast from the loudspeakers
0:46
in the Near-End room, where it goes directly back into the microphone and is transmitted back to the Far-End.
0:51
"Can you hear me?"
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In addition, this direct path is only one of many ways the voice could go to re-enter the microphone.
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It could bounce off of the wall, off a person in your room, it could bounce off a wall,
1:03
against a water bottle, against a wall, off the back of your head, onto the ceiling and downa gain.
1:06
These are known as acoustic reflections, or echoes. Since these acoustic paths all have different physical lengths,
1:14
they result in different time delays from the loudspeaker to the microphone.
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And as the sound travels through the air and bounces of various surfaces,
1:22
it becomes distorted as different frequencies are absorbed and attenuated.
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And all of this is sent back to the far end.
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The average latency of telephone audio is about 50 ms, which means that as the Far-End talker speaks,
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he’ll hear all these reflections of his own voice returned to him 100 ms later...
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Are you hearing this echo? Because I’m having a lot of trouble understanding what you’re saying.
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...which is guaranteed to make anyone tongue-tied...
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My side is really echoey...
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A natural solution to this would be to simply turn down the volume
1:52
on the return signal while the Far-End is talking,
1:55
but the problem with that is that means that everyone in the Near-End room has to wait until the Far-End talker is done.
2:00
Try having a productive business meeting with walkie-talkies and you’ll see that this kind of one-at-a-time
2:06
communication isn’t an option. So that's where AEC comes in.
2:09
AEC eliminates the return echo while preserving the Near-End talkers.
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This may sound like a simple thing, and it’s easy to take it for granted.
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Most people use it all the time without realizing it – whenever you use a speakerphone on your home telephone,
2:23
or Skype with PC Speakers you’re using AEC devices.
2:27
You don’t notice what’s happening because, well, that’s the point. But take it away and you’ll notice it then.
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So how does AEC work? For most people, a good answer would be: Magic.
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Just be happy that it works and go about your business. For you, you want more answers.
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In the next section we’ll take a look inside the AEC component at all the various sub-systems
2:48
that comprise this complete speech enhancement system.
Lesson Description
Intro to Acoustic Echo Canceler
2m 55s
Learn why the Acoustic Echo Canceler is necessary in a conference telephone call.
Tips and Definitions
Intro to Acoustic Echo Canceler
2m 55s
Near End: A local conference room with at least one microphone, speaker, and AEC system.
Far End: The remote caller, speaking from a car, hotel room, etc.
Acoustic Reflection: The path a sound takes as it bounces off of various surfaces in a room, also known as an echo. Along the way the sound is distorted and attenuated.
Downloads and Links
Intro to Acoustic Echo Canceler
2m 55s