What is the reason of that 1 kilo ohm connected to the microphone? Why always too high resistors are used? I couldn't find any explanation. How do we calculate these values?
Answer
The microphone is an electret type, which needs a bias for the capacitor, which it basically is. Some electret microphones also have an amplifier built-in, which also needs power. The larger the resistor from \$V_{CC}\$ the larger the voltage drop caused by the supply current, though for an unamplified electret the current is low and the resistor may be bigger.
A too small resistor will cause the signal to be attenuated. \$V_{CC}\$ is ground for AC signals and a small resistor will cause too much current to go that way.
In practice you'll often see higher resistor values, like 10k\$\Omega\$.
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