The iPhone and iPad come with a very powerful audio library in the form of CoreAudio. It's fully featured, extremely flexible and consistently written. With a good knowledge of CoreAudio, you can make your audio processing dreams come true.
So you've read Apple's blurb and you're excited, time to crack open CoreAudio and find out that CoreAudio is written in C, it doesn't use object orientation and there's almost no documentation. It's also closed source and very unforgiving for the uninitiated.
This component is an objective-C library that wraps around CoreAudio and includes a comprehensive PDF guide of how to work with it to create MIDI based iOS apps.
Loading and parsing a MIDI file using CoreMidi: I'll show you how to load a MIDI file using CoreMidi and then access the MIDI events (Note, Tempo, Time Signature, etc...) individually. This puts you in full control and gives you access to all the information the file contains. I also clearly explain how the MIDI file fits together and what the important MIDI messages mean.
Lots of background information: In the tutorial I don't just explain how the example project works. I also give lots of background information and useful tips when processing MIDI files. I explain: bitwise operations, hex and binary, General Midi, how the percussion track work and much more! In fact the guide alone is over 5000 words long!
Writing a fully functional MIDI player: Step by step, I'll explain how to interpret the sequence of messages you retrieved from the MIDI file. The MIDI player uses multi-threading to play the sequence of MIDI messages in real-time. The MIDI clock class ensures that the MIDI file plays smoothly at the correct tempo. The MIDI player provides easy to use callback functions which give you access to all MIDI events in real-time. If you need events which I've aren't included it's easy to extend the framework to support all existing MIDI messages.
Audio Manager provides multi-timbral playback: CoreAudio on the iPhone only comes with a mono-timbral sampler. This means that you can only play your MIDI notes using one instrument sound. The Audio Manager which is included in the tutorial makes it easy to play your MIDI file using up to 10 instruments using a custom SoundFont. I show step by step how to setup a complex audio graph. I'll also show you how to set up the instruments based on information provided in the MIDI file. Doing this provides a rich sound as demonstrated in the video.
Putting it all together: In the final part of the tutorial I'll show how you can put all this together to create a rich MIDI based animation. The animation visualizes the notes as circles traveling from left to right across the screen. The vertical position of the circle depends on the value of the note. Notes pulse based on the metronome beat. Sharps and flats are circles with a random fill. This is a simple example but it could easily provide the basis of a cool game or MIDI playing app.
More than just a tutorial: The sample project, provided with the tutorial, provides a solid framework for your CoreMidi iOS project. The license allows you to use the framework in any number of your own projects. You can use this project as a learning exercise to learn CoreAudio and CoreMidi or base your whole project on the code.
This tutorial took me well over 100 hours to research and write. The information contained in this project just isn't available on the internet. If you're planning to write an app based on CoreMidi it's guaranteed to save you a substantial amount of time.