I have a problem with understanding a text's paragraph about the use of FET as a preamplifier. It claims that it reduces the coupling noise for an electret microphone before it is amplified in the next stage. Here is that section:
The electret microphone has a very high output impedance because in practical microphones the capacitance of the diaphragm is very low. This requires a very high impedance load for the microphone. To prevent noise pickup by the high-input impedance amplifiers, an FET preamplifier is provided within the microphone and provides a low output impedance.
What is the text trying to explain here? The FET in the capsule for preamplification already has a very very high input impedance. So it can already pickup noise. What is the point of saying "to prevent noise pickup by the high-input impedance amplifiers" here? It seems to me if the noise pickup issue is due to the "high-input impedance"; then by adding a preamplifer FET they are again coupling the mic capacitor to a high-input impedance isn't it?
I don't understand how they mitigate the noise by adding another high input impedance device(FET) if the noise is related to high input impedance.