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Add butterworth low & high pass filters
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Nikita Lisitsa 2026-07-19 02:16:29 +03:00
parent b39475d3ac
commit e94490cf95
2 changed files with 71 additions and 0 deletions
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12
libs/audio/include/psemek/audio/effect/butterworth.hpp Normal file
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#pragma once
#include <psemek/audio/stream.hpp>
namespace psemek::audio
{
// Second-order
stream_ptr butterworth_low_pass(stream_ptr stream, float cutoff_frequency);
stream_ptr butterworth_high_pass(stream_ptr stream, float cutoff_frequency);
}

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