For Windows Vista and newer, you can no longer use the Media Control Interface, Microsoft has a new Core Audio API that you must access to interface with audio hardware in these newer operating systems.

Ray Molenkamp wrote a nice managed wrapper for interfacing with the Core Audio API here: Vista Core Audio API Master Volume Control

Since I needed to be able to mute the microphone from XP, Vista and Windows 7 I wrote a little Windows Microphone Mute Library which uses Ray s library on the newer operating systems and parts of Gustavo Franco s MixerNative library for Windows XP and older.

You can download the source of a whole application which has muting the microphone, selecting it as a recording device, etc.

http://www.codeguru.com/csharp/csharp/cs_graphics/sound/article.php/c10931/

you can use MCI (Media Control Interface) to access mics and change their volume system wise. Check the code below it should be setting volume to 0 for all system microphones. Code is in c; check pinvoke for details on how to translate this code to c#

#include "mmsystem.h"
...
void MuteAllMics()
{
    HMIXER hmx; 
    mixerOpen(&hmx, 0, 0, 0, 0); 

    // Get the line info for the wave in destination line 
    MIXERLINE mxl; 
    mxl.cbStruct = sizeof(mxl); 
    mxl.dwComponentType = MIXERLINE_COMPONENTTYPE_DST_WAVEIN; 
    mixerGetLineInfo((HMIXEROBJ)hmx, &mxl, MIXER_GETLINEINFOF_COMPONENTTYPE); 

    // find the microphone source line connected to this wave in destination 
    DWORD cConnections = mxl.cConnections; 
    for (DWORD j=0; j<cConnections; j++)
    { 
        mxl.dwSource = j; 
        mixerGetLineInfo((HMIXEROBJ)hmx, &mxl, MIXER_GETLINEINFOF_SOURCE); 

        if (MIXERLINE_COMPONENTTYPE_SRC_MICROPHONE == mxl.dwComponentType) 
        {
            // Find a volume control, if any, of the microphone line 
            LPMIXERCONTROL pmxctrl = (LPMIXERCONTROL)malloc(sizeof MIXERCONTROL); 
            MIXERLINECONTROLS mxlctrl = 
            {
                sizeof mxlctrl, 
                mxl.dwLineID, 
                MIXERCONTROL_CONTROLTYPE_VOLUME, 
                1, 
                sizeof MIXERCONTROL, 
                pmxctrl
            }; 
            if (!mixerGetLineControls((HMIXEROBJ) hmx, &mxlctrl, MIXER_GETLINECONTROLSF_ONEBYTYPE))
            { 
                DWORD cChannels = mxl.cChannels; 
                if (MIXERCONTROL_CONTROLF_UNIFORM & pmxctrl->fdwControl) 
                    cChannels = 1; 

                LPMIXERCONTROLDETAILS_UNSIGNED pUnsigned = (LPMIXERCONTROLDETAILS_UNSIGNED) 
                malloc(cChannels * sizeof MIXERCONTROLDETAILS_UNSIGNED); 
                MIXERCONTROLDETAILS mxcd = 
                {
                    sizeof(mxcd), 
                    pmxctrl->dwControlID, 
                    cChannels, 
                    (HWND)0, 
                    sizeof MIXERCONTROLDETAILS_UNSIGNED,
                    (LPVOID) pUnsigned
                }; 
                mixerGetControlDetails((HMIXEROBJ)hmx, &mxcd, MIXER_SETCONTROLDETAILSF_VALUE); 

                // Set the volume to the middle (for both channels as needed) 
                //pUnsigned[0].dwValue = pUnsigned[cChannels - 1].dwValue = (pmxctrl->Bounds.dwMinimum+pmxctrl->Bounds.dwMaximum)/2; 
                // Mute 
                pUnsigned[0].dwValue = pUnsigned[cChannels - 1].dwValue = 0;
                mixerSetControlDetails((HMIXEROBJ)hmx, &mxcd, MIXER_SETCONTROLDETAILSF_VALUE); 

                free(pmxctrl); 
                free(pUnsigned); 
            } 
            else 
            {
                free(pmxctrl); 
            }
        }
    } 
    mixerClose(hmx); 
}

here you can find more code on this topic

hope this helps, regards

I have several microphones in win7 and class WindowsMicrophoneMuteLibrary.CoreAudioMicMute is incorrect in this case.

so I change the code and works great because now his cup Whistle all microphones and not just in the last recognized by win7.

I am attaching the new class to put in place.

http://www.developpez.net/forums/d1145354/dotnet/langages/csharp/couper-micro-sous-win7/