How can I connect sidechain signal to AudioProcessorGraph?

Development
1

I am a beginner at JUCE and trying to make a sidechain compressor.
Following this JUCE tutorial(JUCE: Tutorial: Cascading plug-in effects
),
I tried to connect nodes to get a buffer from the Sidechain signal but I cannot get any signals from the sidechain bus.

Could someone help me?

I set buses properties like the following code.

TestAudioProcessor::DuckerAudioProcessor()
     : AudioProcessor (BusesProperties()
                       .withInput("Input", juce::AudioChannelSet::stereo(), true)
                       .withOutput("Output", juce::AudioChannelSet::stereo(), true)
                       .withInput("Sidechain", juce::AudioChannelSet::stereo(), true)),
        mainProcessor(new juce::AudioProcessorGraph())
                    
{
}

And I created nodes and connected them at the main prepareToPlay function.

The following code is how I created nodes.

    mainProcessor->clear();
    
    //Create nodes
    
    audioInputNode = mainProcessor->addNode(std::make_unique<AudioGraphIOProcessor>(AudioGraphIOProcessor::audioInputNode));
    audioOutputNode = mainProcessor->addNode(std::make_unique<AudioGraphIOProcessor>(AudioGraphIOProcessor::audioOutputNode));
    
    CompressorProcessorNode = mainProcessor->addNode(std::make_unique<CompressorProcessor<float>>());

Then I connected them together.

    for (int channel = 0; channel <2; ++channel)
    {
        mainProcessor->addConnection ({ { audioInputNode->nodeID,  channel },
                                        { CompressorProcessorNode->nodeID, channel } });
        
        mainProcessor->addConnection ({ { CompressorProcessorNode->nodeID, channel },
                                        { audioOutputNode->nodeID, channel } });
        
        //sideChain signal
        mainProcessor->addConnection ({ { audioInputNode->nodeID,  channel+2 },
                                        { CompressorProcessorNode->nodeID, channel +2 } });
    }

Is something wrong with me?
Thank you.

2

My guess is that the AudioProcessorGraph needs to be informed about the number of inputs and outputs it should have. You could try calling mainProcessor->setPlayConfigDetails (4, 2, sampleRate, blockSize) during the prepareToPlay of the DuckerAudioProcessor, and before creating the node connections. It’s probably also a good idea to check the result of addConnection and to output some debugging text if adding the connection fails.