Simulating a microphone with a microcontroller?
I would suggest an attenuator and a DC block.  Microphone outputs are nowhere near 3.3 volts, so you will probably need to divide that down 100x to 1000x with a voltage divider.  A DC blocking cap forms a high pass filter, so just figure out what the source and load impedances are, calculate the cutoff frequency (f = 1/RC) and figure out what cap value will give you a cutoff lower than the lowest frequency you're interested in.  Generally something in the ballpark of 1 to 100 uF should work.