main.cpp

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(500.0); // set a pretty low cut off frequency to make it really noticeable
    }
    void releaseResources() override
    {
        // nothing to do here, we don't have anything to release    
    }
    void getNextAudioBlock(const juce::AudioSourceChannelInfo& bufferToFill) override
    {
        bufferToFill.clearActiveBufferRegion();
        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 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;
};