juce_StateVariableFilter.h

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 /*
  ==============================================================================
 
   This file is part of the JUCE library.
   Copyright (c) 2022 - Raw Material Software Limited
 
   JUCE is an open source library subject to commercial or open-source
   licensing.
 
   By using JUCE, you agree to the terms of both the JUCE 7 End-User License
   Agreement and JUCE Privacy Policy.
 
   End User License Agreement: www.juce.com/juce-7-licence
   Privacy Policy: www.juce.com/juce-privacy-policy
 
   Or: You may also use this code under the terms of the GPL v3 (see
   www.gnu.org/licenses).
 
   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.
 
  ==============================================================================
*/
 
namespace juce::dsp::StateVariableFilter
{
    template <typename NumericType>
    struct Parameters;
 
    template <typename SampleType>
    class Filter
    {
    public:
        //==============================================================================
        using NumericType = typename SampleTypeHelpers::ElementType<SampleType>::Type;
 
        using ParametersPtr = typename Parameters<NumericType>::Ptr;
 
        //==============================================================================
       #ifndef DOXYGEN
        [[deprecated ("The classes in the StateVariableFilter namespace are deprecated. you should "
                     "use the equivalent functionality in the StateVariableTPTFilter class.")]]
        Filter() : parameters (new Parameters<NumericType>) { reset(); }
 
        [[deprecated ("The classes in the StateVariableFilter namespace are deprecated. you should "
                     "use the equivalent functionality in the StateVariableTPTFilter class.")]]
        Filter (ParametersPtr parametersToUse) : parameters (std::move (parametersToUse)) { reset(); }
       #endif
 
        Filter (const Filter&) = default;
 
        Filter (Filter&&) = default;
 
        //==============================================================================
        void prepare (const ProcessSpec&) noexcept     { reset(); }
 
        void reset() noexcept                          { s1 = s2 = SampleType {0}; }
 
        void snapToZero() noexcept                     { util::snapToZero (s1); util::snapToZero (s2); }
 
        //==============================================================================
        typename Parameters<NumericType>::Ptr parameters;
 
        //==============================================================================
        template <typename ProcessContext>
        void process (const ProcessContext& context) noexcept
        {
            static_assert (std::is_same_v<typename ProcessContext::SampleType, SampleType>,
                           "The sample-type of the filter must match the sample-type supplied to this process callback");
 
            if (context.isBypassed)
                processInternal<true, ProcessContext> (context);
            else
                processInternal<false, ProcessContext> (context);
        }
 
        SampleType JUCE_VECTOR_CALLTYPE processSample (SampleType sample) noexcept
        {
            switch (parameters->type)
            {
                case Parameters<NumericType>::Type::lowPass:  return processLoop<false, Parameters<NumericType>::Type::lowPass>  (sample, *parameters); break;
                case Parameters<NumericType>::Type::bandPass: return processLoop<false, Parameters<NumericType>::Type::bandPass> (sample, *parameters); break;
                case Parameters<NumericType>::Type::highPass: return processLoop<false, Parameters<NumericType>::Type::highPass> (sample, *parameters); break;
                default: jassertfalse;
            }
 
            return SampleType{0};
        }
 
    private:
        //==============================================================================
        template <bool isBypassed, typename Parameters<NumericType>::Type type>
        SampleType JUCE_VECTOR_CALLTYPE processLoop (SampleType sample, Parameters<NumericType>& state) noexcept
        {
            y[2] = (sample - s1 * state.R2 - s1 * state.g - s2) * state.h;
 
            y[1] = y[2] * state.g + s1;
            s1   = y[2] * state.g + y[1];
 
            y[0] = y[1] * state.g + s2;
            s2   = y[1] * state.g + y[0];
 
            return isBypassed ? sample : y[static_cast<size_t> (type)];
        }
 
        template <bool isBypassed, typename Parameters<NumericType>::Type type>
        void processBlock (const SampleType* input, SampleType* output, size_t n) noexcept
        {
            auto state = *parameters;
 
            for (size_t i = 0 ; i < n; ++i)
                output[i] = processLoop<isBypassed, type> (input[i], state);
 
           #if JUCE_DSP_ENABLE_SNAP_TO_ZERO
            snapToZero();
           #endif
 
            *parameters = state;
        }
 
        template <bool isBypassed, typename ProcessContext>
        void processInternal (const ProcessContext& context) noexcept
        {
            auto&& inputBlock  = context.getInputBlock();
            auto&& outputBlock = context.getOutputBlock();
 
            // This class can only process mono signals. Use the ProcessorDuplicator class
            // to apply this filter on a multi-channel audio stream.
            jassert (inputBlock.getNumChannels()  == 1);
            jassert (outputBlock.getNumChannels() == 1);
 
            auto n = inputBlock.getNumSamples();
            auto* src = inputBlock .getChannelPointer (0);
            auto* dst = outputBlock.getChannelPointer (0);
 
            switch (parameters->type)
            {
                case Parameters<NumericType>::Type::lowPass:  processBlock<isBypassed, Parameters<NumericType>::Type::lowPass>  (src, dst, n); break;
                case Parameters<NumericType>::Type::bandPass: processBlock<isBypassed, Parameters<NumericType>::Type::bandPass> (src, dst, n); break;
                case Parameters<NumericType>::Type::highPass: processBlock<isBypassed, Parameters<NumericType>::Type::highPass> (src, dst, n); break;
                default: jassertfalse;
            }
        }
 
        //==============================================================================
        std::array<SampleType, 3> y;
        SampleType s1, s2;
 
        //==============================================================================
        JUCE_LEAK_DETECTOR (Filter)
    };
 
    enum class StateVariableFilterType
    {
        lowPass,
        bandPass,
        highPass
    };
 
    //==============================================================================
    template <typename NumericType>
    struct Parameters  : public ProcessorState
    {
        //==============================================================================
        using Type = StateVariableFilterType;
 
        //==============================================================================
        Type type = Type::lowPass;
 
        void setCutOffFrequency (double sampleRate, NumericType frequency,
                                 NumericType resonance = static_cast<NumericType> (1.0 / MathConstants<double>::sqrt2)) noexcept
        {
            jassert (sampleRate > 0);
            jassert (resonance > NumericType (0));
            jassert (frequency > NumericType (0) && frequency <= NumericType (sampleRate * 0.5));
 
            g  = static_cast<NumericType> (std::tan (MathConstants<double>::pi * frequency / sampleRate));
            R2 = static_cast<NumericType> (1.0 / resonance);
            h  = static_cast<NumericType> (1.0 / (1.0 + R2 * g + g * g));
        }
 
        //==============================================================================
        using Ptr = ReferenceCountedObjectPtr<Parameters>;
 
        //==============================================================================
        Parameters() = default;
        Parameters (const Parameters& o) : g (o.g), R2 (o.R2), h (o.h) {}
        Parameters& operator= (const Parameters& o) noexcept    { g = o.g; R2 = o.R2; h = o.h; return *this; }
 
        //==============================================================================
        NumericType g   = static_cast<NumericType> (std::tan (MathConstants<double>::pi * 200.0 / 44100.0));
        NumericType R2  = static_cast<NumericType> (MathConstants<double>::sqrt2);
        NumericType h   = static_cast<NumericType> (1.0 / (1.0 + R2 * g + g * g));
    };
 
} // namespace juce::dsp::StateVariableFilter