Okay, I am going to try to make this totally not a "plz send teh codez kthxbai"

I am considering an app which takes sound (eventually an audio track) and applies an audio filter to it.

So I can play sounds with AudioServicesPlaySystemSound via AudioToolbox framework just fine.

What I need is a very simple example of how I might take a sound and apply (for instance) midrange boost etc. Actually the kind of alteration is irrelevant -- if I can get my head around how the alteration is done I can figure out the rest. I am just finding both docs and examples of altering audio in code to be very scarce.

Thanks for any help!