While many great points have been raised, and even though it's interesting as a proof of concept, I think it's just a waste of time.
An Arduino UNO is not suited for this task, especially if the OP just wants his/her project working and has limited experience with the topic.
@OP, you still haven't told us what you really want to do. Having the Arduino read an input voltage and output the same voltage is not really useful, and only causes signal degradation.
What kind of "real time audio processing" do you want to do?
Edit: it seems like OP has opened a new thread on the same topic: http://forum.arduino.cc/index.php?topic=599651.0