Sidechain Inputs

Routing custom audio streams to a plug-in.

Overview of Sidechain Inputs

If applicable, plug-ins may choose to enable sidechain inputs. If a sidechain is enabled, a menu is added to the plug-in's header that allows the user to choose an interface or bus as the sidechain, or "key input". Once enabled, the plug-in will be able to access sidechain input just like any other input signal. Currently, DAE is limited to mono sidechain inputs.

Adding a Sidechain Input to an Effect

Setting up a sidechain input is fairly straight forward. You will want to add a physical address within your context structure, and then "describe" the sidechain in Describe.

Context Structure:

//=============================
// Component context definitions
//=============================

// Context structure
struct SMyPlugIn_Alg_Context
{
   [...]
   int32_t  * mSideChainP;
   [...]
};

// Physical addresses within the context
enum EDemoDist_Alg_PortID
{
    [...]
    ,MyPlugIn_AlgFieldID_SideChain  = AAX_FIELD_INDEX (SDemoDist_Alg_Context, mSideChainP)
    [...]
};

Describe:

// ***************************************************************************
// ROUTINE: DescribeAlgorithmComponent
// Algorithm component description
// ***************************************************************************
static void DescribeAlgorithmComponent( AAX_IComponentDescriptor * outDesc )
{
    AAX_Result                  err = AAX_SUCCESS;

    [...]
    err = outDesc.AddSideChainIn(eDemoDist_AlgFieldID_SideChain);
    [...]
    properties->AddProperty ( AAX_eProperty_SupportsSideChainInput, true );
    [...]
}

Todo:

Is properties->AddProperty ( AAX_eProperty_SupportsSideChainInput, true ) even necessary?!?! I believe I saw a p.i. that does not declare this...

In order to tell whether there is sidechain information available to your plug-in, check for a null pointer within your algorithm's process function. The sidechain channel will show up as an additional stem from the original stem format you declare. That is to stay, for a stereo plug-in, the sidechain channel will be the third channel passed in.

//==============================================================================
// Processing function definition
//==============================================================================

void
AAX_CALLBACK
MyPlugIn_AlgorithmProcessFunction (
    SMyPlugIn_Alg_Context * const   inInstancesBegin [],
    const void *                    inInstancesEnd)
{
    [...]
    int32_t sideChainChannel = *instance->mSideChainP;   
    float * AAX_RESTRICT sideChainInput = 0;
    if ( sideChainChannel )
      sideChainInput = instance->mInputPP [sideChain]Channel;
    [...]
}

Collaboration diagram for Sidechain Inputs: