iPhone audio Filter Question

Question

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!

Answer 1

Unfortunately, anything beyond basic recording and playing of PCM data requires digging into the more murky depths of Core Audio. I would probably start by looking at the Core Audio Overview documentation from Apple. They provide an entire mechanism with Audio Units for writing a signal processor or "effect units" that sit in the audio processing graph.

Answer 2

See example 6 here:

http://www.modejong.com/iPhone/

The example implements a fade out effect using the ExtAudioFile API. The example shows the basics of what you want to do, you would need to implement the mid range boost DSP logic, but this at least gets you started. Just looking at the CoreAudio docs is going to be a big waste of time because there are so many things documented there, just knowing where to being is the hard part.