HRESULT WINAPI CreateCaptureAudioStateMonitorForCategory(
  AUDIO_STREAM_CATEGORY category,
  _Out_ IAudioStateMonitor **audioStateMonitor
);

HRESULT RegisterForSoundLevelChanges() 
{ 
HRESULT hr = S_OK; 

// Create a new AudioStateMonitor for the GameChat category, if needed, and 
// register for callbacks. 
if (m_audioStateMonitor == nullptr) 
{ 
hr = CreateCaptureAudioStateMonitorForCategoryAndDeviceRole( 
AudioCategory_GameChat, ERole::eCommunications, 
g_audioStateMonitor.put()); 
if (SUCCEEDED(hr)) 
{ 
// Optional "context" parameter is not used in this example, 
// and is set to nullptr. 
hr = g_audioStateMonitor->RegisterCallback(OnAudioStateMonitorCallback, nullptr, &m_registration); 
} 
} 

if (FAILED(hr)) 
{ 
// g_audioStateMonitor is a smart pointer, so if an IAudioStateMonitor was 
// allocated, setting the smart pointer to null invokes the Release method 
// which will decrement its usage count and ensure that the object is properly 
// destroyed. 
g_audioStateMonitor = nullptr; 
} 
return hr; 
}