Are there any frameworks or open-source code that would simplify the process of implementing a real-time oscilloscope (time-domain audio visualisation) in OSX?
Ideally, I want to display a simple animated view representing the audio signal being input by the microphone input.
The easiest way to do this is to use a QCView. It's pretty easy to find QC compositions that display a bar graph display of the audio output.
Look at a language called Pd (Pure Data). It's the free version of Max/MSP. It's the easiest way to do anything with audio. One of the classes is in fact an oscilloscope. Simply draw a line from the output of your sound source (it can be your mic, a sound file, or a live oscillator) to the oscilloscope and bathe in the visual output glory!
the SurfaceVertexProgram example is a nice demonstration of how to do an oscilloscope using OpenGL. the example is a bit out-dated (you have to build up a new xcode project), but functions and demonstrates very useful techniques.