Maybe have a look at this...
I've never used @ogiewon's Hubduino software, but this looks like a good option. If this is your fist go-round with a baby, you'll eventually get to the stage where they can sleep through the night, but still have some fussy periods when the cant find their pacifier, etc. For those of us that can hear, you learn to "screen out" those little whimpers and whines. It's not until they get into a full blown cry that you probably need to get out of bed. Using something like an arduino, you could use the onboard microcontroller to "filter" microphone input. The downside: this could take some time and it sounds like you need sleep right now. The up side: Something like this could give you the best long-term results.
Hopefully ogiewon can weigh in. If you're interested in this and he doesn't reply, I'd post something over in the hubduino thread.
