I want to record audio and apply custom-built sound effect filters, then play it back.
Are Audio Units and Audio Queue Services the API I'm looking for? Or are there other APIs which fit this purpose better?
Also, I've been told Audio Units can't be customized on iOS so there are just a few pre-made effects available. Is this true?
Audio Units is the most useful API for building effects processing under iOS. iOS 5 added several new types of filter and effect units. You can add your own custom DSP effects inside certain audio unit buffer callbacks.