On a MacBook, I can be in a Zoom Meeting and speak into the MacBook Mic, while also listening to the meeting via the MacBook speakers. How is it possible for the mic to only receive my voice (and not also the sound of the meeting coming out of the speakers)?
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Its a cool little amplifier called the difference amplifier. It is one of the first amps you learn about in Electrical engineering.
The difference amp has 2 inputs. What happens is it will take the 2 inputs, subtract them from one another through signal combining and only the difference between the 2 inputs gets actually amplified.
It compares the output to the input and if sees the same thing, it get attenuated (volume is greatly lowered).
This is also how people on a helicopter can talk through their headsets. Both head sets are picking up the sound of the rotors so they cancel each other out, but only my mic picks up my voice, not your mic so you clearly hear my voice over the rotors. Its a neat little device and just requires a couple transistors to make one.
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