If you want to do audio programming you pretty much need to learn C. C++ isn't required by any means, although Apple does provide some convenience objects for common tasks (like ring buffers) that are written in C++. There are also some nice non-apple audio libraries using C++ that will take care of things like oscillators and filters for you. But really, you can get by on C depending on what you want to make.
If you've been doing Objective-C you probably have a pretty good handle on at least half of C. From there you need to make sure you understand pointers / pointer arithmetic and memory management.
I taught a class recently on creating music / art applications for iOS:
http://www.mat.ucsb.edu/594CR
There are sample projects on the website that cover MIDI, OSC, Bonjour, audio and more. They aren't really commented since I went through them in class, but I did try to make each example as simple as I possibly could. In general they are simpler and more direct than other examples you'll find on the web. And I'm happy to answer questions.
Good luck! - Charlie
PS - join the core audio mailing list.
but if anyone fancies giving me any advise / other good forums for audio programming id be grateful!
