This function requires the Wave driver involved in the call is used to detect silence. The frequencies in the lineMonitorTone structure pointed to by lpToneList must all be zero. If silence is detected, a line_MonitorTone message is sent to the application. Call lineMonitorTone with lpToneList is set to NULL to cancel silence detection.

LONG
WINAPI
lineMonitorTone(
HCALL hCall, 
LPLINEMONITORTONE const lpToneList, 
DWORD dwNumEntries 
);