when I’m on loudspeaker during a phone call on my phone, why don’t the speaker and the microphone create an infinite loop of echo?

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when I’m on loudspeaker during a phone call on my phone, why don’t the speaker and the microphone create an infinite loop of echo?

In:

https://electronics.stackexchange.com/questions/24470/avoiding-echo-feedback-on-speaker-phones-how

Here is an article that you’ll probably find useful. Essentially there is usually an algorithm that will cut out frequencies to avoid feedback. Sometimes it doesn’t work. I’m guessing there is also gain attenuation (variable mic input) goin on to help avoid feedback.

There are several ways this is handled, but the most interresting to me are:

Phase Locked Loops (PLLs)

Basically, the system “knows” what is being sent out from the speaker, and these frequencies can be timed and very precisely removed from the microphone input. In the past, this was done using analog circuitry. It’s the same technology that has kept major rock concerts from being ear-splitting feedback since the invention of the loudspeaker.

Because processors are so fast now, the same functionality can now be done in software in the digital world.