This program is equivalent to the "Microphone Select" check box of Windows Volume Control for Recording. The Microphone Select control is one of the items of the MIXERCONTROL_CONTROLTYPE_MIXER or MIXERCONTROL_CONTROLTYPE_MUX controls of the MIXERLINE_COMPONENTTYPE_DST_WAVEIN destination audio line. It belongs to the list controls (MIXERCONTROL_CT_CLASS_LIST), which provide single-select or multiple-select states for complex audio lines. It uses the MIXERCONTROLDETAILS_BOOLEAN structure to retrieve and set control properties. Whenever the check box is clicked, CSelectDlg::amdSetMicSelectValue() is called to set the Microphone Select value accordingly. The MM_MIXM_CONTROL_CHANGE message is received once the state of the Microphone Select control has changed. In this case, CSelectDlg::amdGetMicSelectValue() is called to retrieve the current value of the Microphone Select control and update the state of the check box accordingly.