Core Audio (iOS 5.1) Reverb2 properties do not exist, error code -10877

Question

I am playing with Apple's sample project "LoadPresetDemo". I have added the reverb audio unit AudioUnit kAudioUnitSubType_Reverb2 to the graph, which is the only iOS reverb available. In the CoreAudio header file "AudioUnitParameters.h", it states that Reverb2 should respond to these parameters:

enum {
    // Global, CrossFade, 0->100, 100
    kReverb2Param_DryWetMix = 0,
    // Global, Decibels, -20->20, 0
    kReverb2Param_Gain = 1,
    // Global, Secs, 0.0001->1.0, 0.008
    kReverb2Param_MinDelayTime = 2,
    // Global, Secs, 0.0001->1.0, 0.050
    kReverb2Param_MaxDelayTime = 3,
    // Global, Secs, 0.001->20.0, 1.0
    kReverb2Param_DecayTimeAt0Hz = 4,
    // Global, Secs, 0.001->20.0, 0.5
    kReverb2Param_DecayTimeAtNyquist = 5,
    // Global, Integer, 1->1000
    kReverb2Param_RandomizeReflections = 6,
};

After the AUGraph has been initialized and started, everything compiles, I hear sound.

Next, I alter the kReverb2Param_DryWetMix parameter (changing to full wet mix):

AudioUnitSetParameter(_reverbUnit, kAudioUnitScope_Global, 0, kReverb2Param_DryWetMix, 100.0f, 0);

All good, I hear sound with full wet mixed reverb.

Now hear is where I run into issues. When trying to alter any parameter other than kReverb2Param_DryWetMix I get error code -10877. It seems as if these other parameters listed in the header file do not actually exist.

For example, calling

AudioUnitSetParameter(_reverbUnit, kAudioUnitScope_Global, 0, kReverb2Param_DecayTimeAtNyquist, 20.0f, 0)

Throws the -10877 error.

Is this a bug? Have I omitted any audio frameworks? Have I not imported specific audio headers?

The current audio frameworks included are AVFoundation and AudioToolbox. The current audio imports are

#import <AudioToolbox/AudioToolbox.h>
#import <AVFoundation/AVFoundation.h>
#import <CoreAudio/CoreAudioTypes.h>

I have scoured google with no solution. I know I have problems when the Google route fails. Any help would be greatly appreciated.

Note: I tested with simulator and iPhone 4S device, same problem.

UPDATE: I have tried

AudioUnitGetParameter(_reverbUnit, kReverb2Param_DecayTimeAtNyquist, kAudioUnitScope_Global, 0, &value)

and it returns a value of 0.500000, which means the property does exist. So what am I doing wrong in setting the value?

Answer 1

Doh! I realize that I was confusing AudioUnitSetParameter with AudioUnitSetProperty, including their parameters. Man, subtle but evil.