It require cap at the input. Initially, I thought just to post a link:http://interface.khm.de/index.php/lab/experiments/arduino-realtime-audio-processing/ (I like this drawings, post it all the time).
Does hZ in electricity matter for this kind of thing? (hZ or Hertz, is electricity flowing through a wire, at all times, not sure about AC, the electricity is off for 60 times a second and on for 60 times a second. I guess AC is a bit slower than that to consider it AC.)
Is there anything I have to change in schematic #3? Also, if I use a resistor of different resistance, will it decrease performance?
and I guess DC is just 60Hz.