What is echo cancellation

What is echo cancellation?

Echo cancellation removes unwanted echoes in phone calls—typically caused when a speaker’s voice is reflected back through the phone’s microphone. This can happen through:

  • Acoustic echo – speaker audio picked up by the same device’s mic
  • Line echo – electrical interference between transmit and receive lines

What is echo?

Echo, in a telephony context, is a situation where a person’s voice in the outgoing stream from a handset microphone is reflected back to the same person in the incoming return stream to the handset’s loudspeaker.

Echo is typically created in one of 2 ways:

  • voice coming through a phone’s loudspeaker gets picked up by the same phone’s microphone (sometimes called acoustic echo),
  • electrical signals travelling over a sending wire get picked up by an adjacent receiving wire (sometimes called line echo); this can happen in a few different ways, but it is typically to do with the electrical characteristic of the sending, receiving, and intervening devices.

 

Why / when does it matter?

Echo cancellation with IP Phone and 3CX App

Even though we do not realize it, there are many situations where echo is present in a telephone conversation. So the question we REALLY need to ask here is “When is Echo a problem?”

Echo is a problem when it interferes with our understanding of another person’s voice in a phone call, or when it confuses a person who is speaking because he hears himself on the line. If we think this through, we can quite easily deduce that the problem is “delay” – more accurately, the delay between the spoken word in the outbound stream and its reflection in the return stream.

If the delay is less than 25 milliseconds, it’s almost undetectable to the human ear–indeed, if you ask a user if he hears any echo in such a situation, you will almost certainly get a “no” for an answer. If the delay is a little longer, say in the region of 55 milliseconds, the user experience is very much like having 2 people saying the same thing at the same time, like a duet performance; other users describe it like talking in a completely empty room. This level of echo or delay, though noticeable, is very well tolerated and normally does not induce user complaints.

Once a delay increases beyond 55 milliseconds it becomes increasingly annoying and distracting to users, making it quite difficult to carry on a conversation. For a normal user, the echo of their own voice effectively breaks down the call by interrupting their thought process.

Echo Cancellation vs Echo Suppression

There are two methods for dealing with echo: echo cancellation and echo suppression.

  • Echo cancellation analyzes the return audio stream and removes duplicated sound before it’s sent.
  • Echo suppression mutes one side of the call when the other is speaking—effective, but more disruptive to the conversation flow.