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- #ifndef FILTERS_BIQUAD_H
- #define FILTERS_BIQUAD_H
-
- #include <cmath>
- #include <utility>
-
- #include "AL/al.h"
- #include "math_defs.h"
-
-
- /* Filters implementation is based on the "Cookbook formulae for audio
- * EQ biquad filter coefficients" by Robert Bristow-Johnson
- * http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
- */
- /* Implementation note: For the shelf filters, the specified gain is for the
- * reference frequency, which is the centerpoint of the transition band. This
- * better matches EFX filter design. To set the gain for the shelf itself, use
- * the square root of the desired linear gain (or halve the dB gain).
- */
-
- enum class BiquadType {
- /** EFX-style low-pass filter, specifying a gain and reference frequency. */
- HighShelf,
- /** EFX-style high-pass filter, specifying a gain and reference frequency. */
- LowShelf,
- /** Peaking filter, specifying a gain and reference frequency. */
- Peaking,
-
- /** Low-pass cut-off filter, specifying a cut-off frequency. */
- LowPass,
- /** High-pass cut-off filter, specifying a cut-off frequency. */
- HighPass,
- /** Band-pass filter, specifying a center frequency. */
- BandPass,
- };
-
- template<typename Real>
- class BiquadFilterR {
- /* Last two delayed components for direct form II. */
- Real z1{0.0f}, z2{0.0f};
- /* Transfer function coefficients "b" (numerator) */
- Real b0{1.0f}, b1{0.0f}, b2{0.0f};
- /* Transfer function coefficients "a" (denominator; a0 is pre-applied). */
- Real a1{0.0f}, a2{0.0f};
-
- public:
- void clear() noexcept { z1 = z2 = 0.0f; }
-
- /**
- * Sets the filter state for the specified filter type and its parameters.
- *
- * \param type The type of filter to apply.
- * \param gain The gain for the reference frequency response. Only used by
- * the Shelf and Peaking filter types.
- * \param f0norm The reference frequency normal (ref_freq / sample_rate).
- * This is the center point for the Shelf, Peaking, and
- * BandPass filter types, or the cutoff frequency for the
- * LowPass and HighPass filter types.
- * \param rcpQ The reciprocal of the Q coefficient for the filter's
- * transition band. Can be generated from calc_rcpQ_from_slope
- * or calc_rcpQ_from_bandwidth as needed.
- */
- void setParams(BiquadType type, Real gain, Real f0norm, Real rcpQ);
-
- void copyParamsFrom(const BiquadFilterR &other)
- {
- b0 = other.b0;
- b1 = other.b1;
- b2 = other.b2;
- a1 = other.a1;
- a2 = other.a2;
- }
-
-
- void process(Real *dst, const Real *src, int numsamples);
-
- void passthru(int numsamples) noexcept
- {
- if(LIKELY(numsamples >= 2))
- {
- z1 = 0.0f;
- z2 = 0.0f;
- }
- else if(numsamples == 1)
- {
- z1 = z2;
- z2 = 0.0f;
- }
- }
-
- /* Rather hacky. It's just here to support "manual" processing. */
- std::pair<Real,Real> getComponents() const noexcept
- { return {z1, z2}; }
- void setComponents(Real z1_, Real z2_) noexcept
- { z1 = z1_; z2 = z2_; }
- Real processOne(const Real in, Real &z1_, Real &z2_) const noexcept
- {
- Real out{in*b0 + z1_};
- z1_ = in*b1 - out*a1 + z2_;
- z2_ = in*b2 - out*a2;
- return out;
- }
- };
-
- using BiquadFilter = BiquadFilterR<float>;
-
- /**
- * Calculates the rcpQ (i.e. 1/Q) coefficient for shelving filters, using the
- * reference gain and shelf slope parameter.
- * \param gain 0 < gain
- * \param slope 0 < slope <= 1
- */
- inline float calc_rcpQ_from_slope(float gain, float slope)
- { return std::sqrt((gain + 1.0f/gain)*(1.0f/slope - 1.0f) + 2.0f); }
-
- inline double calc_rcpQ_from_slope(double gain, double slope)
- { return std::sqrt((gain + 1.0/gain)*(1.0/slope - 1.0) + 2.0); }
-
- /**
- * Calculates the rcpQ (i.e. 1/Q) coefficient for filters, using the normalized
- * reference frequency and bandwidth.
- * \param f0norm 0 < f0norm < 0.5.
- * \param bandwidth 0 < bandwidth
- */
- inline float calc_rcpQ_from_bandwidth(float f0norm, float bandwidth)
- {
- const float w0{al::MathDefs<float>::Tau() * f0norm};
- return 2.0f*std::sinh(std::log(2.0f)/2.0f*bandwidth*w0/std::sin(w0));
- }
-
- inline double calc_rcpQ_from_bandwidth(double f0norm, double bandwidth)
- {
- const double w0{al::MathDefs<double>::Tau() * f0norm};
- return 2.0*std::sinh(std::log(2.0)/2.0*bandwidth*w0/std::sin(w0));
- }
-
- #endif /* FILTERS_BIQUAD_H */
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