How to develop an iphone app with reverb functionality?

I am developing an iPhone application (like Audio Processing). I have to give some effect to the audios. If it is desktop app, many options are there. We can get good examples and full project like audacity. But I want to develop for iPhone.

I got an app with reverb option; (take a look at following link). Just I watch the "video", I did not test this application in my iPhone device.
http://www.appstorehq.com/reverb-iphone-89870/app

My question is; How can I develop the app with reverb functionality ? Is there any documentation for that ? If it is, just share with us.

NOTE: We can use AudioUnit to develop the app with reverb functionality (I am not clear with this.).

EDIT: I don't like to use any third party library.

If anybody having knowledge about this, please share with us.

Thanks.