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Adding the Wet Mix Property

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[The feature associated with this page, Windows Media Player SDK, is a legacy feature. It has been superseded by MediaPlayer. MediaPlayer has been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer instead of Windows Media Player SDK, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

You must add the code to provide the additional property for the effect level.

The section Adding Properties to the Sample Audio DSP Plug-in provides details about how to add a new property using Visual C++. This section shows you how to add the code manually. This entails adding code in the same three places where you modified the code for the delay time property.

Add the prototypes for the get_wetmix and put_wetmix methods immediately following the other property method prototypes in Echo.h. Use the following syntax:

STDMETHOD(get_wetmix)(double *pVal);
STDMETHOD(put_wetmix)(double newVal);

Now, add the implementation for each method immediately following the other property implementations in Echo.cpp. The following example shows the code for both methods:

// Property get to retrieve the wet mix value by using the public interface.
STDMETHODIMP CEcho::get_wetmix(double *pVal)
{
    if ( NULL == pVal )
    {
        return E_POINTER;
    }

    *pVal = m_fWetMix;

    return S_OK;
}

// Property put to store the wet mix value by using the public interface.
STDMETHODIMP CEcho::put_wetmix(double newVal)
{
    m_fWetMix = newVal;

    // Calculate m_fDryMix
    m_fDryMix = 1.0 - m_fWetMix;
    
    return S_OK;
}

Notice that the implementation of put_wetmix includes the code to calculate the correct value for m_fDryMix. Each time a new value is specified for m_fWetMix, this calculation is required.

Add the following code in the interface definition just after the code for the delay methods in Echo.idl:

HRESULT get_wetmix([out] double *pVal);
HRESULT put_wetmix([in] double newVal);

Echo Sample Properties