It is wired up like in this tutorial (https://www.instructables.com/id/Make-Your-Own-Spy-Bug-Arduino-Voice-Recorder/), I know your reservations about this but it was as simplified as possible for me to understand.
I do not know what biased to half the rail is.
I would presume it is DC?
This is the wiring schematic I used. Minus the LED and Tactile switch.
The microphone is this one (https://www.ebay.co.uk/itm/Max9814-Electret-Microphone-Amplifier-Module-Auto-Gain-Control-For-Arduino-C16/283401758790?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649). I presumed it had some limited amplification.
The code appears to do nothing, doesn't create a file on the SD card or produce any messages.
Thank you.