setting Input property for USB headsets

Hi

 

With two different USB microphones we’ve tried, we’re getting ‘who?’ when setting kAudioDevicePropertyVolumeScalar with the following lines of code:

theStatus = AudioDeviceGetPropertyInfo (

                                                _inputDeviceID, i, true,

                                                kAudioDevicePropertyVolumeScalar,

                                                NULL, &isWritable );

 

          if(theStatus != kAudioHardwareNoError)

          {

                  LOG(TR_ERROR, " SetMicLevel() AudioDeviceGetPropertyInfo error: %4.4s", (char*)&theStatus);

          }

 

My question is, do USB headsets generally not support setting an input level through Core Audio? Is it a hardware deficiency or a driver problem?  Is checking for ‘who?’ in this case the best way to determine if this functionality is present?

 

Thank you,

 

Neal