C / C++ / MFC

Long SumOfSamples = 0
Long SumOfSquaredDifferences = 0

// First determine the average sound level
// I don't know whether audio data is represented as unsigned or signed values - 
// you may have to look at the values in a data block to decide what to use!
For count = 1 to numberSamplesInBlock
	SumOfSamples += soundSample[count]

AverageSoundLevel = SumOfSamples / numberSamplesInBlock

// Now work out the average of how far every sample is from the average level
For count = 1 to numberSamplesInBlock
	ThisSampleDifference = sample[count] - AverageSoundLevel
	SumOfSquaredDifferences += ThisSampleDifference * ThisSampleDifference

AverageDifference = SquareRoot(SumOfSquaredDifferences) / numberSamplesInBlock

// Now decide whether the data block is loud or soft or in-between
If AverageDifference < softSoundThreshold
	Display "The Sound Is Soft"
Else if AverageDifference > loudSoundThreshold
	Display "The Sound Is Loud"
Else
	Display "The Sound Is Between Soft And Loud Limits"

// Determine the softSoundThreshold and loudSoundThreshold by recording 
// sounds using the microphone and looking at their AverageDifference values

V_shr wrote:

thanks a lot , it was useful to me

Call "CoCreateInstance" to retrieve a pointer to the "IWiaDevMgr" interface.
Use the "IWiaDevMgr::EnumDeviceInfo" method of the "IWiaDevMgr" interface to obtain a pointer to the "IEnumWIA_DEV_INFO" interface. 
Use "IEnumWIA_DEV_INFO" interface to obtain "IWiaPropertyStorage" interface pointers for each WIA device enumerated.
Use "IWiaPropertyStorage" interface to inspect the device information properties of each device and save the "WIA_DIP_DEV_ID" property from the desired device.
Use the "DeviceID" property with the "IWiaDevMgr::CreateDevice" method in the "IWiaDevMgr" interface to create a WIA device object. The "IWiaDevMgr::CreateDevice method" provides the application with the pointer to the IWiaItem interface of the root item of the specified device.

example for create a device :

HRESULT CreateWiaDevice( IWiaDevMgr *pWiaDevMgr, BSTR bstrDeviceID, IWiaItem **ppWiaDevice )
    {
        //
        // Validate arguments
        //
        if (NULL == pWiaDevMgr || NULL == bstrDeviceID || NULL == ppWiaDevice)
        {
            return E_INVALIDARG;
        }

        //
        // Initialize out variables
        //
        *ppWiaDevice = NULL;

        //
        // Create the WIA Device
        //
        HRESULT hr = pWiaDevMgr->CreateDevice( bstrDeviceID, ppWiaDevice );

        //
        // Return the result of creating the device
        //
        return hr;
    }

for (i=0; i<10; i++)
{
  if(capGetDriverDescription(i, szDeviceName, sizeof(szDeviceName),
	szDeviceVersion, sizeof(szDeviceVersion)) )
  {
    if(strcmp(szDeviceName, "MyDeviceName") == 0)
    {
      SendMessage( hwndVideo, WM_CAP_DRIVER_CONNECT, i, 0L);
    }
  }
}

// get the selected driver
SendMessage( hwndSelCapDrvDlg_LBox, LB_GETSELITEMS, 1, sel);

// get the selected driver
SendMessage( hwndSelCapDrvDlg_LBox, LB_GETSELITEMS, 1, &sel);

SendMessage( hwndVideo, WM_CAP_DRIVER_CONNECT, i, 0L);

for (i=0; i<10; i++)
{
  if(capGetDriverDescription(i, szDeviceName, sizeof(szDeviceName),	szDeviceVersion, sizeof(szDeviceVersion)) )
  {
    if(strcmp(szDeviceName, "MyDeviceName") == 0)
    {
      SendMessage( hwndVideo, WM_CAP_DRIVER_CONNECT, i, 0L);
      break;
    }
  }
}

int TForm1::EnumCapDrv() // enumerate the installed capture drivers

SendMessage( hwndVideo, WM_CAP_DRIVER_CONNECT, sel, 0L);

SendMessage( hwndSelCapDrvDlg_LBox, LB_GETSELITEMS, 1, sel);

SendMessage( hwndSelCapDrvDlg_LBox, LB_GETSELITEMS, 1, &sel);