Audio merging on AudioClip and save

Hi everyone, i'm trying to merge an audio record with himself with different pitch and then save it into a file. The basic idea is the user record his voice and then the application process it and generates an audio that sounds like a crowd of people screaming. I try a lot of things but i can't merge the audio channels and save them into a single flile (no better the format).

Can everyone help me?

Thanks a lot! and my apologies by my english.