[LAD] Audio Trigger

Hi all, I need to use a microphone input as a trigger. In other words my idea is to connect a switch to the microphone input. In this way, when the switch is turned on it generates a spike in the captured track. I would like to create a program that trigger an event every spike it receives. I succeed in capturing the mic input through a simple program that uses alsa driver, but I don't know how to "parse" the raw data to search for the spikes. Any hints? Second question: on a "full duplex" sound card, can I capture at 8 bit, mono, 22.050 bit/s , and on the same time playback at 16 bit, stereo, 44.100 ? Thank you! Lorenzo