main.cpp

#include <JuceHeader.h>

class Noise : public juce::AudioSource
{
public:
    void prepareToPlay(int samplesPerBlockExpected, double sampleRate) override
    {
        // initialise the filter object
        juce::dsp::ProcessSpec spec;
        spec.maximumBlockSize = samplesPerBlockExpected;
        spec.sampleRate = sampleRate;
        spec.numChannels = 1;
        filter.prepare(spec);
        filter.setCutoffFrequency(500);
        // initialise LFO with a sine wave
        auto wavetablefunc = [](float x)
        {
            return std::sin(x);
        };
        osc.initialise(wavetablefunc, 1024);
        osc.setFrequency(0.5); // LFO runs at 0.5 Hz
        osc.prepare(spec);
    }
    void releaseResources() override
    {
        // nothing to do here, we don't have anything to release    
    }
    void getNextAudioBlock(const juce::AudioSourceChannelInfo& bufferToFill) override
    {
        for (int i = 0; i < bufferToFill.numSamples; ++i)
        {
            float noise = juce::jmap(rgen.nextFloat(),0.0f,1.0f,-1.0f,1.0f) * 0.1f; // generate output sample
            float cutoff = juce::jmap(osc.processSample(0.0f), -1.0f, 1.0f, 500.0f, 8000.0f);
            filter.setCutoffFrequency(cutoff);
            float out = filter.processSample(0, noise);
            // copy to all output channels
            for (int j=0;j<bufferToFill.buffer->getNumChannels();++j)
            {
                bufferToFill.buffer->setSample(j, i, out);
            }
        }
    }
private:
    juce::Random rgen;
    juce::dsp::StateVariableTPTFilter<float> filter;
    juce::dsp::Oscillator<float> osc;
};

//==============================================================================
int main (int argc, char* argv[])
{
    juce::ScopedJuceInitialiser_GUI gui_init; // even if this isn't a GUI app, the Juce message manager needs to be running
    juce::AudioDeviceManager aman;
    aman.initialiseWithDefaultDevices(0, 2); // 0 inputs, 2 outputs for the audio
    juce::AudioSourcePlayer noisePlayer;
    Noise noiseSource;
    noisePlayer.setSource(&noiseSource);
    aman.addAudioCallback(&noisePlayer);

    juce::Thread::sleep(5000); // keep the audio playing for 5 seconds (5000 milliseconds)
    return 0;
}