|Sensitivity circuit, adjust values as needed|
Calibrate the sensitivity control based on the sound source to improve the sensitivity and quality of the signal. The microphone will be the most sensitive when the value is at zero ohms. R1 is actually an optional resistor as shown. It's purpose is to limit the voice sensitivity, for example, a 10K resistor will resist the voice signal coming from microphone more as compared to the 1K resistor.