With a condenser mic you need to cap couple it to one of the A/D channels and provide some VDD drive to the mic. To do that you need to provide ~ +5 volts thru a 10k to the mic directly. I don't believe there will be enough signal for the A/D to measure as there is usually only ~ .01 volts peak to peak from the mic. You will probably need an amplifier in series with it to drive the A/D.