Prompt:

Generate a proof-of-concept C++ code for an audio processing plugin based on the following requirements: granular synthesis, low latency playback, dry-wet signal

Reponse:

The implementation of an audio processing plugin involves the use of several frameworks or libraries that provide access to audio processing capabilities. To build this plugin, I’ll use JUCE, a framework that is widely used for creating audio plugins, and is compatible with VST/AU/RTAS formats for audio plugins.

Note: A real-life implementation of a granular synthesis engine would take into account much more factors and would be much larger than this example.

#include "../JuceLibraryCode/JuceHeader.h"

class GranularAudioProcessor  : public AudioProcessor
{
public:
    GranularAudioProcessor()
        : parameters(*this, nullptr, Identifier("GranularAudio"),
        {
            std::make_unique<AudioParameterFloat>("drywet", "Dry/Wet", 0.0f, 1.0f, 0.5f)
        })
    {
    }
    
    void prepareToPlay (double sampleRate, int samplesPerBlock) override
    {
        // Prepare granular synthesis engine here...
    }
    
    void processBlock (AudioBuffer<float>& buffer, MidiBuffer& midiMessages) override
    {
        const int totalNumInputChannels  = getTotalNumInputChannels();
        const int totalNumOutputChannels = getTotalNumOutputChannels();
        
        // Clear any channels that happen to be unused
        for (int i = totalNumInputChannels; i < totalNumOutputChannels; ++i)
            buffer.clear (i, 0, buffer.getNumSamples());

        float* channelData = buffer.getWritePointer(0);
        float dryWet = *parameters.getRawParameterValue("drywet");

        // The actual granular synthesis would be implemented here, with a low-latency algorithm.
        // This loop just demonstrates the concept of mixing the dry/wet signals.
        for (int i = 0; i < buffer.getNumSamples(); i++)
        {
            float drySignal = channelData[i];
            float wetSignal = /* granularSynthesisEngine.processSample(drySignal) */;  // This would be the output of the granular synthesis
            
            // Mix dry and wet signals
            channelData[i] = drySignal * (1.0 - dryWet) + wetSignal * dryWet;
        }
    }

    AudioProcessorValueTreeState parameters;

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (GranularAudioProcessor)
};

PluginHostType::jucePlugInClientCurrentWrapperType = AudioProcessor::wrapperType_VST3;
AudioProcessor* JUCE_CALLTYPE createPluginFilter()
{
    return new GranularAudioProcessor();
}

In this example, GranularAudioProcessor is the main class that performs audio processing. The plugin has one parameter, “drywet”, which controls the mix of the original signal (dry) and the processed signal (wet).

The prepareToPlay method is called before audio processing begins, and should be used to initialize the granular synthesis engine.

The processBlock method is called to process each block of audio samples. It gets a reference to the audio buffer and a midi buffer (which is not used in this case). The buffer contains the input samples in its channels, and should be overwritten with the output samples.

The createPluginFilter function is the entry point for the plugin. It must return a new instance of the AudioProcessor subclass.

Please replace the commented granular synthesis processing parts with a real granular synthesis algorithm.

Prompt

Create a granular synthesis algorithm.

Response

Creating a granular synthesis algorithm involves several steps and it’s a complex topic. However, I’ll provide a simple illustrative example of how it could be done.

In granular synthesis, an audio signal is divided into small chunks or “grains”, each of which can be manipulated independently. This allows for interesting effects such as time stretching and pitch shifting. A granular synthesizer usually has parameters like grain size, grain rate, and grain pitch.

Note: Real-life implementations are much more complex, with envelope shaping for each grain, overlapping grains for smooth sound, randomized parameters for a more organic sound, and much more.

Here’s a simplified code snippet of a granular synthesis algorithm, to be included in the previous JUCE-based plugin example.

class GranularSynth
{
public:
    GranularSynth() 
        : grainSize(4410),   // default 100ms at 44100Hz
          grainRate(2205),   // default one grain every 50ms
          grainPitch(1.0f),  // default no pitch shift
          buffer(grainSize),
          writePos(0)
    {}

    void setGrainSize(int size) { grainSize = size; }
    void setGrainRate(int rate) { grainRate = rate; }
    void setGrainPitch(float pitch) { grainPitch = pitch; }

    float processSample(float sample)
    {
        // Write sample to circular buffer
        buffer[writePos] = sample;
        writePos = (writePos + 1) % grainSize;

        // Every grainRate samples, start a new grain
        if (writePos % grainRate == 0)
        {
            grainPos = writePos;
            grainSpeed = grainPitch;
        }

        // Read from the current grain with pitch shift
        int readPos = (int) (grainPos * grainSpeed);
        float output = buffer[(writePos - readPos + grainSize) % grainSize];

        // Advance the grain position, wrapping around at grainSize
        grainPos = (grainPos + 1) % grainSize;

        return output;
    }

private:
    int grainSize;
    int grainRate;
    float grainPitch;

    std::vector<float> buffer;
    int writePos;
    int grainPos;
    float grainSpeed;
};

In this example, the granular synthesizer has three parameters: grain size, grain rate, and grain pitch. These control the size of the grains, the rate at which new grains are started, and the pitch shift applied to the grains, respectively.

The processSample method processes one sample at a time. It writes the sample to a circular buffer, then checks if it’s time to start a new grain. If so, it initializes the grain position and speed according to the grain pitch. Finally, it reads the output from the current grain, applying the pitch shift, and advances the grain position.

This algorithm is quite simple and doesn’t create a smooth or high-quality sound. A real granular synthesis algorithm would use window functions to shape the amplitude of the grains, overlapping grains to avoid discontinuities, and probably more sophisticated techniques for pitch shifting. Nevertheless, it demonstrates the basic principle of granular synthesis.