mixer.cpp

class MixerCallBack : public AudioIODeviceCallback
{
public:
    std::vector<float> channelGains;
    std::vector<float> channelPans;
    MixerCallBack()
    {
        channelGains.resize(16);
        channelPans.resize(16);
    }
    void audioDeviceIOCallback(const float **inputChannelData, int numInputChannels, float **outputChannelData, int numOutputChannels, int numSamples) override
    {
        // zero output buffer before starting to sum into it
        for (int i=0;i<numOutputChannels;++i)
        {
            for (int j=0;j<numSamples;++j)
            {
                outputChannelData[i][j] = 0.0f;
            }
        }
        for (int i=0;i<numInputChannels;++i)
        {
            for (int j=0;j<numSamples;++j)
            {
                float s = inputChannelData[i][j];
                float gain = channelGains[i];
                float gain_l = 1.0-channelPans[i];
                float gain_r = channelPans[i];
                outputChannelData[0][j] += s * gain * gain_l;
                outputChannelData[1][j] += s * gain * gain_r;
            }
        }
    }
    
    void audioDeviceAboutToStart(juce::AudioIODevice *device) override
    {
        
    }
    
    void audioDeviceStopped() override
    {}
    
};

void test_mixer_cb()
{
    ScopedJuceInitialiser_GUI mm;
    AudioDeviceManager man;
    man.initialiseWithDefaultDevices(8, 2);
    MixerCallBack mcb;
    mcb.channelGains[0] = 1.0;
    mcb.channelPans[0] = 0.5;
    man.addAudioCallback(&mcb);
    Thread::sleep(2000);
}