Question

I want to modify the apple’s sample code of auriotouch to generate the waveform from and audio file instead of rendering the waveform from the mic input. I tried to do it, but i am not able to understand where and what changes to make. Can anyone guide me on how it can be achieved.

Thanks,

Answer 1

Look inside the render callback for a function named AudioUnitRender

The render callback happens whenever the speakers are hungry for data.

IIRC A.T. simply grabs however many samples are required from the microphone using this function

Of course, the first time round it will fail because there will be nothing waiting

Anyway, just comment out this function and instead fill the buffer yourself with samples from your file ( which I think you would probably want to load into memory in advance, probably don’t want fileIO clogging a high priority thread )

that means you will probably need to create some sort of AudioFile class, and pass a reference to an instance of this class when you set up the render callback. that way you will be able to access the data from within this render callback ( which is a vanilla C function, ie not a member of a class, so it has no other way to access class data — unless you want to do something horrible with file-level variables ).

make sure you create this AudioFile* audiofile NONATOMIC if it is a property, you don’t want your render callback to be kept waiting because some other thread is inside the object and consequently has a lock on it.