59 lines
1.5 KiB
C++
59 lines
1.5 KiB
C++
#include <psemek/audio/effect/butterworth.hpp>
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#include <psemek/audio/effect/filter.hpp>
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#include <psemek/audio/constants.hpp>
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#include <psemek/math/constants.hpp>
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namespace psemek::audio
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{
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stream_ptr butterworth_low_pass(stream_ptr stream, float cutoff_frequency)
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{
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float omega = 2.f * static_cast<float>(math::pi) * cutoff_frequency * audio::inv_frequency;
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omega = 2.f * audio::frequency * std::tan(omega / 2.f);
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float gamma = 2.f * audio::frequency / omega;
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float sqrt2 = std::sqrt(2.f);
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float a0 = gamma * gamma + sqrt2 * gamma + 1.f;
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float a1 = - 2.f * gamma * gamma + 2.f;
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float a2 = gamma * gamma - sqrt2 * gamma + 1.f;
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float b0 = 1.f;
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float b1 = 2.f;
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float b2 = 1.f;
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a1 /= a0;
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a2 /= a0;
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b0 /= a0;
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b1 /= a0;
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b2 /= a0;
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return linear_filter(std::move(stream), {a1, a2}, {b0, b1, b2});
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}
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stream_ptr butterworth_high_pass(stream_ptr stream, float cutoff_frequency)
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{
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float omega = 2.f * static_cast<float>(math::pi) * (audio::frequency / 2.f - cutoff_frequency) * audio::inv_frequency;
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omega = 2.f * audio::frequency * std::tan(omega / 2.f);
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float gamma = 2.f * audio::frequency / omega;
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float sqrt2 = std::sqrt(2.f);
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float a0 = gamma * gamma + sqrt2 * gamma + 1.f;
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float a1 = 2.f * gamma * gamma - 2.f;
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float a2 = gamma * gamma - sqrt2 * gamma + 1.f;
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float b0 = 1.f;
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float b1 = - 2.f;
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float b2 = 1.f;
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a1 /= a0;
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a2 /= a0;
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b0 /= a0;
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b1 /= a0;
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b2 /= a0;
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return linear_filter(std::move(stream), {a1, a2}, {b0, b1, b2});
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}
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}
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