juce_StateVariableTPTFilter.cpp

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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
{
 
//==============================================================================
template <typename SampleType>
StateVariableTPTFilter<SampleType>::StateVariableTPTFilter()
{
    update();
}
 
template <typename SampleType>
void StateVariableTPTFilter<SampleType>::setType (Type newValue)
{
    filterType = newValue;
}
 
template <typename SampleType>
void StateVariableTPTFilter<SampleType>::setCutoffFrequency (SampleType newCutoffFrequencyHz)
{
    jassert (isPositiveAndBelow (newCutoffFrequencyHz, static_cast<SampleType> (sampleRate * 0.5)));
 
    cutoffFrequency = newCutoffFrequencyHz;
    update();
}
 
template <typename SampleType>
void StateVariableTPTFilter<SampleType>::setResonance (SampleType newResonance)
{
    jassert (newResonance > static_cast<SampleType> (0));
 
    resonance = newResonance;
    update();
}
 
//==============================================================================
template <typename SampleType>
void StateVariableTPTFilter<SampleType>::prepare (const ProcessSpec& spec)
{
    jassert (spec.sampleRate > 0);
    jassert (spec.numChannels > 0);
 
    sampleRate = spec.sampleRate;
 
    s1.resize (spec.numChannels);
    s2.resize (spec.numChannels);
 
    reset();
    update();
}
 
template <typename SampleType>
void StateVariableTPTFilter<SampleType>::reset()
{
    reset (static_cast<SampleType> (0));
}
 
template <typename SampleType>
void StateVariableTPTFilter<SampleType>::reset (SampleType newValue)
{
    for (auto v : { &s1, &s2 })
        std::fill (v->begin(), v->end(), newValue);
}
 
template <typename SampleType>
void StateVariableTPTFilter<SampleType>::snapToZero() noexcept
{
    for (auto v : { &s1, &s2 })
        for (auto& element : *v)
            util::snapToZero (element);
}
 
//==============================================================================
template <typename SampleType>
SampleType StateVariableTPTFilter<SampleType>::processSample (int channel, SampleType inputValue)
{
    auto& ls1 = s1[(size_t) channel];
    auto& ls2 = s2[(size_t) channel];
 
    auto yHP = h * (inputValue - ls1 * (g + R2) - ls2);
 
    auto yBP = yHP * g + ls1;
    ls1      = yHP * g + yBP;
 
    auto yLP = yBP * g + ls2;
    ls2      = yBP * g + yLP;
 
    switch (filterType)
    {
        case Type::lowpass:   return yLP;
        case Type::bandpass:  return yBP;
        case Type::highpass:  return yHP;
        default:              return yLP;
    }
}
 
//==============================================================================
template <typename SampleType>
void StateVariableTPTFilter<SampleType>::update()
{
    g  = static_cast<SampleType> (std::tan (juce::MathConstants<double>::pi * cutoffFrequency / sampleRate));
    R2 = static_cast<SampleType> (1.0 / resonance);
    h  = static_cast<SampleType> (1.0 / (1.0 + R2 * g + g * g));
}
 
//==============================================================================
template class StateVariableTPTFilter<float>;
template class StateVariableTPTFilter<double>;
 
} // namespace juce::dsp