JUCE/modules/juce_dsp/frequency/juce_Windowing.cpp

/*
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*/

namespace juce::dsp
{

template <typename FloatType>
static FloatType ncos (size_t order, size_t i, size_t size) noexcept
{
    return std::cos (static_cast<FloatType> (order * i)
                      * MathConstants<FloatType>::pi / static_cast<FloatType> (size - 1));
}

template <typename FloatType>
WindowingFunction<FloatType>::WindowingFunction (size_t size, WindowingMethod type, bool normalise, FloatType beta)
{
    fillWindowingTables (size, type, normalise, beta);
}

template <typename FloatType>
void WindowingFunction<FloatType>::fillWindowingTables (size_t size, WindowingMethod type,
                                                        bool normalise, FloatType beta) noexcept
{
    windowTable.resize (static_cast<int> (size));
    fillWindowingTables (windowTable.getRawDataPointer(), size, type, normalise, beta);
}

template <typename FloatType>
void WindowingFunction<FloatType>::fillWindowingTables (FloatType* samples, size_t size,
                                                        WindowingMethod type, bool normalise,
                                                        FloatType beta) noexcept
{
    switch (type)
    {
        case rectangular:
        {
            for (size_t i = 0; i < size; ++i)
                samples[i] = static_cast<FloatType> (1);
        }
        break;

        case triangular:
        {
            auto halfSlots = static_cast<FloatType> (0.5) * static_cast<FloatType> (size - 1);

            for (size_t i = 0; i < size; ++i)
                samples[i] = static_cast<FloatType> (1.0) - std::abs ((static_cast<FloatType> (i) - halfSlots) / halfSlots);
        }
        break;

        case hann:
        {
            for (size_t i = 0; i < size; ++i)
            {
                auto cos2 = ncos<FloatType> (2, i, size);
                samples[i] = static_cast<FloatType> (0.5 - 0.5 * cos2);
            }
        }
        break;

        case hamming:
        {
            for (size_t i = 0; i < size; ++i)
            {
                auto cos2 = ncos<FloatType> (2, i, size);
                samples[i] = static_cast<FloatType> (0.54 - 0.46 * cos2);
            }
        }
        break;

        case blackman:
        {
            constexpr FloatType alpha = 0.16f;

            for (size_t i = 0; i < size; ++i)
            {
                auto cos2 = ncos<FloatType> (2, i, size);
                auto cos4 = ncos<FloatType> (4, i, size);

                samples[i] = static_cast<FloatType> (0.5 * (1 - alpha) - 0.5 * cos2 + 0.5 * alpha * cos4);
            }
        }
        break;

        case blackmanHarris:
        {
            for (size_t i = 0; i < size; ++i)
            {
                auto cos2 = ncos<FloatType> (2, i, size);
                auto cos4 = ncos<FloatType> (4, i, size);
                auto cos6 = ncos<FloatType> (6, i, size);

                samples[i] = static_cast<FloatType> (0.35875 - 0.48829 * cos2 + 0.14128 * cos4 - 0.01168 * cos6);
            }
        }
        break;

        case flatTop:
        {
            for (size_t i = 0; i < size; ++i)
            {
                auto cos2 = ncos<FloatType> (2, i, size);
                auto cos4 = ncos<FloatType> (4, i, size);
                auto cos6 = ncos<FloatType> (6, i, size);
                auto cos8 = ncos<FloatType> (8, i, size);

                samples[i] = static_cast<FloatType> (1.0 - 1.93 * cos2 + 1.29 * cos4 - 0.388 * cos6 + 0.028 * cos8);
            }
        }
        break;

        case kaiser:
        {
            const double factor = 1.0 / SpecialFunctions::besselI0 (beta);
            const auto doubleSize = (double) size;

            for (size_t i = 0; i < size; ++i)
                samples[i] = static_cast<FloatType> (SpecialFunctions::besselI0 (beta * std::sqrt (1.0 - std::pow (((double) i - 0.5 * (doubleSize - 1.0))
                                                                                                                     / ( 0.5 * (doubleSize - 1.0)), 2.0)))
                                                      * factor);
        }
        break;

        case numWindowingMethods:
        default:
            jassertfalse;
            break;
    }

    // DC frequency amplitude must be one
    if (normalise)
    {
        FloatType sum (0);

        for (size_t i = 0; i < size; ++i)
            sum += samples[i];

        auto factor = static_cast<FloatType> (size) / sum;

        FloatVectorOperations::multiply (samples, factor, static_cast<int> (size));
    }
}

template <typename FloatType>
void WindowingFunction<FloatType>::multiplyWithWindowingTable (FloatType* samples, size_t size) const noexcept
{
    FloatVectorOperations::multiply (samples, windowTable.getRawDataPointer(), jmin (static_cast<int> (size), windowTable.size()));
}

template <typename FloatType>
const char* WindowingFunction<FloatType>::getWindowingMethodName (WindowingMethod type) noexcept
{
    switch (type)
    {
        case rectangular:          return "Rectangular";
        case triangular:           return "Triangular";
        case hann:                 return "Hann";
        case hamming:              return "Hamming";
        case blackman:             return "Blackman";
        case blackmanHarris:       return "Blackman-Harris";
        case flatTop:              return "Flat Top";
        case kaiser:               return "Kaiser";
        case numWindowingMethods:
        default: jassertfalse;     return "";
    }
}

template class WindowingFunction<float>;
template class WindowingFunction<double>;

} // namespace juce::dsp