What is meant by “impedance matching”? How is it done? Why is it necessary?
We can talk about the characteristic impedance of an input, which is to say the ratio of voltage to current that it likes to see, or how much it loads down a source. (You can think of this as being an “AC resistance” and you would be mostly right, although it’s actually the absolute magnitude of the vector drawn by the resistive and reactive load components. Dealing with line level signals, reactive components are going to be negligible, though). In general, in this modern world, most equipment has a low impedance output, going into relatively high impedance input. This wastes some amount of power, but because electricity is cheap and it’s possible to build low-Z outputs easily today, this is not a big deal. With microphones, it _is_ a big deal, because the signal levels are very low, and the drive ability poor. As a result, we try and get the best efficiency possible from microphones to get the lowest noise floor.
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