Decimation using LagrangeInterpolator?

General JUCE discussion
1

Is it possible to downsample well using LagrangeInterpolator?

I’m trying to create a very simple class to load a short buffer upon initialisation of the plugin, and then loop it forever. I have files in 96kHz wav so am wanting to be able to downsample these to loop. However, when this happens I get some whining (at different frequencies depending on sample rate). I tried to filter the wav before processing it with my LagrangeInterpolator as I was getting the same effect with my own non filtered 6 point Lagrange interpolator class. Adding a filter didn’t seem to remove the whining much.

Any glaringly obvious things I am doing wrong?

class SamplePlayer
{
    public:
    SamplePlayer()
    {
        currentSample = 0;
    }
    
    void initialise(double fileSampleRate, double newSampleRate, const float *inputBuffer, int numSamplesInFile)
    {
        store.setSize(1, (numSamplesInFile / fileSampleRate) * newSampleRate);
        store.clear();
        
        double speed = fileSampleRate / newSampleRate;
        auto output = store.getWritePointer(0);

        rateConvert.process(speed, inputBuffer, output, (numSamplesInFile / fileSampleRate) * newSampleRate);
    }
    
    float getNextSample()
    {
        ++currentSample;
        if (currentSample >= store.getNumSamples()) {
            currentSample = 0;
        }
        auto read = store.getReadPointer(0);
        return read[currentSample];
    }
    
    void processBuffer(float* const inputBuffer, int numSamples) {
        for (int i=0; i < numSamples; i++)
        {
            inputBuffer[i] = getNextSample();
        }
    }
    
    ~SamplePlayer()
    {
    }
    private:
    int currentSample;
    LagrangeInterpolator rateConvert;
    AudioBuffer<float> store;
};

Thanks,
David

EDIT: Have implemented the r8brain resampler and it works as expected.