real time feature extraction

Hi all. I'm working on a project and I've a problem that don't know how to solve. My application should acquire sound from the PC's sound card (I've this part already done) and should detect in real time sound events based on a threshold. Once the program detect an event, it must extract the information from it for later feature extraction and classification. The thing is that I don´t know how to implement a solution that extract the information of the signal when an event is detected. Any idea?
Thanks in advance.