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.
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