How to Control Microphone Boost/AGC using C++

Question

I want to control my boost/AGC settings on my microphone input. Windows 7 audio properties shows that it has an AGC option.

However when I try to access it via C++ It comes back saying there is no AGC on the device.

I am using DeviceTopology class WASAPI does not have any API to control AGC functionality Here's the code so far:

(Mostly lifted from MSDN forum sample)

    #include <windows.h>
    #include <stdio.h>
    #include <mmdeviceapi.h>
    #include <devicetopology.h>

    HRESULT WalkTreeBackwardsFromPart(IPart *pPart, int iTabLevel = 0);
    HRESULT DisplayVolume(IAudioVolumeLevel *pVolume, int iTabLevel);
    HRESULT DisplayMute(IAudioMute *pMute, int iTabLevel);
    void Tab(int iTabLevel);

    int __cdecl main(void) {
    HRESULT hr = CoInitialize(NULL);
    if (FAILED(hr)) {
        printf("Failed CoInitializeEx: hr = 0x%08x\n", hr);
        return __LINE__;
    }

    // get default render endpoint
    IMMDeviceEnumerator *pEnum = NULL;
    hr = CoCreateInstance(
        __uuidof(MMDeviceEnumerator), NULL, CLSCTX_ALL, __uuidof(IMMDeviceEnumerator),
        (void**)&pEnum
    );
    if (FAILED(hr)) {
        printf("Couldn't get device enumerator: hr = 0x%08x\n", hr);
        CoUninitialize();
        return __LINE__;
    }
    IMMDevice *pDevice = NULL;
    hr = pEnum->GetDefaultAudioEndpoint(eCapture, eConsole, &pDevice);
    if (FAILED(hr)) {
        printf("Couldn't get default render device: hr = 0x%08x\n", hr);
        pEnum->Release();
        CoUninitialize();
        return __LINE__;
    }
    pEnum->Release();

    // get device topology object for that endpoint
    IDeviceTopology *pDT = NULL;
    hr = pDevice->Activate(__uuidof(IDeviceTopology), CLSCTX_ALL, NULL, (void**)&pDT);
    if (FAILED(hr)) {
        printf("Couldn't get device topology object: hr = 0x%08x\n", hr);
        pDevice->Release();
        CoUninitialize();
        return __LINE__;
    }
    pDevice->Release();

    // get the single connector for that endpoint
    IConnector *pConnEndpoint = NULL;
    hr = pDT->GetConnector(0, &pConnEndpoint);
    if (FAILED(hr)) {
        printf("Couldn't get the connector on the endpoint: hr = 0x%08x\n", hr);
        pDT->Release();
        CoUninitialize();
        return __LINE__;
    }
    pDT->Release();

    // get the connector on the device that is
    // connected to
    // the connector on the endpoint
    IConnector *pConnDevice = NULL;
    hr = pConnEndpoint->GetConnectedTo(&pConnDevice);
    if (FAILED(hr)) {
        printf("Couldn't get the connector on the device: hr = 0x%08x\n", hr);
        pConnEndpoint->Release();
        CoUninitialize();
        return __LINE__;
    }
    pConnEndpoint->Release();

    // QI on the device's connector for IPart
    IPart *pPart = NULL;
    hr = pConnDevice->QueryInterface(__uuidof(IPart), (void**)&pPart);
    if (FAILED(hr)) {
        printf("Couldn't get the part: hr = 0x%08x\n", hr);
        pConnDevice->Release();
        CoUninitialize();
        return __LINE__;
    }
    pConnDevice->Release();

    // all the real work is done in this function
    hr = WalkTreeBackwardsFromPart(pPart);
    if (FAILED(hr)) {
        printf("Couldn't walk the tree: hr = 0x%08x\n", hr);
        pPart->Release();
        CoUninitialize();
        return __LINE__;
    }
    pPart->Release();

    CoUninitialize();

    system("pause");
    return 0;
    }

    HRESULT WalkTreeBackwardsFromPart(IPart *pPart, int iTabLevel /* = 0 */) {
    HRESULT hr = S_OK;

    Tab(iTabLevel);
    LPWSTR pwszPartName = NULL;
    hr = pPart->GetName(&pwszPartName);
    if (FAILED(hr)) {
        printf("Could not get part name: hr = 0x%08x", hr);
        return hr;
    }
    printf("Part name: %ws\n", *pwszPartName ? pwszPartName : L"(Unnamed)");
    CoTaskMemFree(pwszPartName);


    // Check AGC settings
    const IID IID_IAudioAutoGainControl = __uuidof(IAudioAutoGainControl);

    IAudioAutoGainControl *aGCcontrol = NULL;
    hr = pPart->Activate(CLSCTX_ALL, IID_IAudioAutoGainControl, (void**)&aGCcontrol);
    if (E_NOINTERFACE == hr) {
          printf("NO AGC CONTROL\n");
        // not a Microphone node
    } else if (FAILED(hr)) {
        printf("Unexpected failure trying to activate IAudioAutoGainControl : hr = 0x%08x\n", hr);
        return hr;
    } else {
        // it's an AGC node...
        printf("HAS AGC CONTROL");
        if (FAILED(hr)) {
            printf("AGC Failed: hr = 0x%08x", hr);
            aGCcontrol->Release();
            return hr;
        }

        aGCcontrol->Release();
    }


    return S_OK;
}

Answer 1

I finally figured out how to do this. I left out some important parts of the code on my sample code above.

To help others that has this same dilemma here's the solution. To compile just replace the MessageBox statements with printf.

The important point here is that when enumerating parts be sure to know if its an input or an output. Otherwise you will never find the part your looking for. This example is looking for the available parts of an eCapture endpoint.

Here's my sources: http://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/9741bae1-c330-4802-9860-2fd202dba797/enumeration-of-available-levels-for-a-specific-installed-sound-card?forum=windowspro-audiodevelopment

Let me know if you have problem compiling it.

#include <windows.h>
#include <stdio.h>
#include <mmdeviceapi.h>
#include <devicetopology.h>

HRESULT WalkTreeBackwardsFromPart(IPart *pPart, int iTabLevel = 0);
HRESULT DisplayVolume(IAudioVolumeLevel *pVolume, int iTabLevel);
HRESULT DisplayMute(IAudioMute *pMute, int iTabLevel);
void Tab(int iTabLevel);

int __cdecl main(void) {
HRESULT hr = CoInitialize(NULL);
if (FAILED(hr)) {
    printf("Failed CoInitializeEx: hr = 0x%08x\n", hr);
    return __LINE__;
}

// get default render endpoint
IMMDeviceEnumerator *pEnum = NULL;
hr = CoCreateInstance(
    __uuidof(MMDeviceEnumerator), NULL, CLSCTX_ALL, __uuidof(IMMDeviceEnumerator),
    (void**)&pEnum
);
if (FAILED(hr)) {
    printf("Couldn't get device enumerator: hr = 0x%08x\n", hr);
    CoUninitialize();
    return __LINE__;
}
IMMDevice *pDevice = NULL;
hr = pEnum->GetDefaultAudioEndpoint(eCapture, eConsole, &pDevice);
if (FAILED(hr)) {
    printf("Couldn't get default capture device: hr = 0x%08x\n", hr);
    pEnum->Release();
    CoUninitialize();
    return __LINE__;
}
pEnum->Release();

// get device topology object for that endpoint
IDeviceTopology *pDT = NULL;
hr = pDevice->Activate(__uuidof(IDeviceTopology), CLSCTX_ALL, NULL, (void**)&pDT);
if (FAILED(hr)) {
    printf("Couldn't get device topology object: hr = 0x%08x\n", hr);
    pDevice->Release();
    CoUninitialize();
    return __LINE__;
}
pDevice->Release();

// get the single connector for that endpoint
IConnector *pConnEndpoint = NULL;
hr = pDT->GetConnector(0, &pConnEndpoint);
if (FAILED(hr)) {
    printf("Couldn't get the connector on the endpoint: hr = 0x%08x\n", hr);
    pDT->Release();
    CoUninitialize();
    return __LINE__;
}
pDT->Release();

// get the connector on the device that is
// connected to
// the connector on the endpoint
IConnector *pConnDevice = NULL;
hr = pConnEndpoint->GetConnectedTo(&pConnDevice);
if (FAILED(hr)) {
    printf("Couldn't get the connector on the device: hr = 0x%08x\n", hr);
    pConnEndpoint->Release();
    CoUninitialize();
    return __LINE__;
}
pConnEndpoint->Release();

// QI on the device's connector for IPart
IPart *pPart = NULL;
hr = pConnDevice->QueryInterface(__uuidof(IPart), (void**)&pPart);
if (FAILED(hr)) {
    printf("Couldn't get the part: hr = 0x%08x\n", hr);
    pConnDevice->Release();
    CoUninitialize();
    return __LINE__;
}
pConnDevice->Release();

// all the real work is done in this function
hr = WalkTreeBackwardsFromPart(pPart);
if (FAILED(hr)) {
    printf("Couldn't walk the tree: hr = 0x%08x\n", hr);
    pPart->Release();
    CoUninitialize();
    return __LINE__;
}
pPart->Release();

CoUninitialize();

system("pause");
return 0;
}

HRESULT WalkTreeBackwardsFromPart(IPart *pPart) {
HRESULT hr = S_OK;

LPWSTR pwszPartName = NULL;
hr = pPart->GetName(&pwszPartName);
if (FAILED(hr)) {
    printf("Could not get part name: hr = 0x%08x", hr);
    return hr;
}
printf("Part name: %ws\n", *pwszPartName ? pwszPartName : L"(Unnamed)");
CoTaskMemFree(pwszPartName);


// Check AGC settings
const IID IID_IAudioAutoGainControl = __uuidof(IAudioAutoGainControl);

IAudioAutoGainControl *aGCcontrol = NULL;
hr = pPart->Activate(CLSCTX_ALL, IID_IAudioAutoGainControl, (void**)&aGCcontrol);
if (E_NOINTERFACE == hr) {
      printf("NO AGC CONTROL\n");
    // not a Microphone node
} else if (FAILED(hr)) {
    printf("Unexpected failure trying to activate IAudioAutoGainControl : hr = 0x%08x\n", hr);
    return hr;
} else {
    // it's an AGC node...
    printf("HAS AGC CONTROL");
    aGCcontrol->SetEnabled(1, NULL);   //Activate it

    if (FAILED(hr)) {
        printf("AGC Failed: hr = 0x%08x", hr);
        aGCcontrol->Release();
        return hr;
    }

    aGCcontrol->Release();
}

// get the list of incoming parts
IPartsList *pOutgoingParts = NULL;
hr = pPart->EnumPartsOutgoing(&pOutgoingParts);

if (E_NOTFOUND == hr) {
    // not an error... we've just reached the end of the path
    MessageBox("No incoming parts at this part\n", MB_OK);
}
if (FAILED(hr)) {
    MessageBox("Couldn't enum outgoing parts", MB_OK);
}
UINT nParts = 0;
hr = pOutgoingParts->GetCount(&nParts);
if (FAILED(hr)) {
    MessageBox("Couldn't get count of outgoing parts", MB_OK);
    pOutgoingParts->Release();
    return hr;
}

// walk the tree on each incoming part recursively
for (UINT n = 0; n < nParts; n++) {
    IPart *pOutgoingPart = NULL;
    hr = pOutgoingParts->GetPart(n, &pOutgoingPart);
    if (FAILED(hr)) {
        MessageBox("Couldn't get part ", MB_OK);
        pOutgoingParts->Release();
        return hr;
    }

    hr = WalkTreeBackwardsFromPart(pOutgoingPart);
    if (FAILED(hr)) {
        MessageBox("Couldn't walk tree on part", MB_OK);
        pOutgoingPart->Release();
        pOutgoingParts->Release();
        return hr;
    }
    pOutgoingPart->Release();
}

pOutgoingParts->Release();

return S_OK;

}