gistfile1.m

// Setting up the Audio Session... 
	// Initialize and configure the audio session, and add an interuption listener
	AudioSessionInitialize(NULL, NULL, sessionInterruptionListener, self);
	
	UInt32 audioCategory = kAudioSessionCategory_PlayAndRecord;
	AudioSessionSetProperty(kAudioSessionProperty_AudioCategory, sizeof(audioCategory), &audioCategory);
	
	// Allow iPod audio to continue to play while the app is active.
	UInt32 flag = 1;
	AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryMixWithOthers, sizeof(flag), &flag);
	
	// Add a property listener to listen to changes to the session
	AudioSessionAddPropertyListener(kAudioSessionProperty_AudioRouteChange, sessionPropertyListener, self);
	
	Float32 preferredBufferSize = 0.00125;
	AudioSessionSetProperty(kAudioSessionProperty_PreferredHardwareIOBufferDuration, sizeof(preferredBufferSize), &preferredBufferSize);
	
	//set the audio session active
	AudioSessionSetActive(YES);

	OSStatus err;

// Now start setting up the graph & nodes
	//create the graph & its only node, which will be of type remoteIO
	NewAUGraph(&graph);	
	AUNode ioNode; 
	
	// First describe the node, graphs are made up of nodes connected together, in this graph there is only one node.
	// the descriptions for the components
	AudioComponentDescription outputDescription;
	outputDescription.componentFlags = 0;
	outputDescription.componentFlagsMask = 0;
	outputDescription.componentType = kAudioUnitType_Output;
	outputDescription.componentSubType = kAudioUnitSubType_RemoteIO;
	outputDescription.componentManufacturer = kAudioUnitManufacturer_Apple;

	// Create the remoteIO node, and open the graph
	err = AUGraphAddNode(graph, &outputDescription, &ioNode);
	NSAssert(err == noErr, @"Failed to add the remoteIO node");

	err = AUGraphOpen (graph);
	NSAssert(err == noErr, @"Opening the audio graph failed");
	
	// Grab an instance of the remoteIO unit from the graph
	AudioUnit ioUnit;
	err = AUGraphNodeInfo(graph, ioNode, NULL, &ioUnit);
	NSAssert(err == noErr, @"NOOO! (couldn't get the node info)");
	
	// Set the audio format on the audio unit instance
	AudioStreamBasicDescription audioFormat;
	memset(&audioFormat, 0, sizeof(audioFormat));
	
	// Let's talk formats for just a sec
	audioFormat.mSampleRate		= 44100.0f;
	audioFormat.mFormatID			= kAudioFormatLinearPCM;
	audioFormat.mFormatFlags		= kAudioFormatFlagsCanonical;
	audioFormat.mFramesPerPacket	= 1;
	audioFormat.mChannelsPerFrame	= 1;
	audioFormat.mBitsPerChannel	= 16;
	audioFormat.mBytesPerPacket	= 2;
	audioFormat.mBytesPerFrame		= 2;
	
	// set the format on the bus coming into the app ... 
	err = AudioUnitSetProperty(ioUnit, 
							   kAudioUnitProperty_StreamFormat, 
							   kAudioUnitScope_Output, 
							   kInputBus, 
							   &audioFormat, 
							   sizeof(audioFormat));
	NSAssert(err == noErr, @"Error setting Output Scope for Bus 1 (from microphone to app)");
	
	// ... and on the bus leaving the app for the mic
	err = AudioUnitSetProperty(ioUnit, 
							   kAudioUnitProperty_StreamFormat, 
							   kAudioUnitScope_Input, 
							   kOutputBus, 
							   &audioFormat, 
							   sizeof(audioFormat));
	NSAssert(err == noErr, @"Error setting Input Scope for Bus 0 (from app to mic)");
	
	
		
	

	// Enable IO from the mic to the app...
	UInt32 one = 1;
	err = AudioUnitSetProperty(ioUnit, 
							   kAudioOutputUnitProperty_EnableIO, 
							   kAudioUnitScope_Input, 
							   kInputBus, // BUS 1
							   &one, 
							   sizeof(one));
	NSAssert(err == noErr, @"Could not enable the Input Scope of Bus 1");
	
	// ... and from the app back out to the mic
	err = AudioUnitSetProperty(ioUnit, 
							   kAudioOutputUnitProperty_EnableIO, 
							   kAudioUnitScope_Output, 
							   kOutputBus, // BUS 0
							   &one, 
							   sizeof(one));
	NSAssert(err == noErr, @"Could not enable the Output Scope of Bus 0");

	
	// This is what doesn't seem to be working
	// ***********************************


	AURenderCallbackStruct playbackCallbackStruct;
	playbackCallbackStruct.inputProc = continuousDisplayOutputCallback;
	continuousCallbackData *cd = (continuousCallbackData *)malloc(sizeof(continuousCallbackData));
	cd->ssb = secondStageBuffer;
	cd->au = &outputAudioUnit;
	playbackCallbackStruct.inputProcRefCon = cd;
	



	// Register a callback with the AUNode
	err = AUGraphSetNodeInputCallback (graph,
									   ioNode,
									   kInputBus,
									   &playbackCallbackStruct);
	
	// continuousDisplayOutputCallback() is never entered! I have an NSLog; return; right at the beginning, 
	// and the app sits silent after initialization, and no audio is acquired.
	// ***********************************	
	
	
	// Now we get to start it all up!
	err = AUGraphInitialize(graph);
	NSAssert(err == noErr, @"Could not initialize audio graph");
		
	err = AUGraphStart(graph);
	NSAssert(err == noErr, @"Could not start audio graph");