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Add textbook filter construction.

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This commit is contained in:
Thomas Harte
2025-11-12 22:06:48 -05:00
parent fa0835abd8
commit c5c6c5ff72
3 changed files with 125 additions and 2 deletions
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2
Components/SID/SID.cpp
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@@ -81,7 +81,7 @@ void SID::write(const Numeric::SizedInt<5> address, const uint8_t value) {
}
void SID::update_filter() {
// TODO!
}
uint8_t SID::read(const Numeric::SizedInt<5> address) {

2
OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme
View File

@@ -62,7 +62,7 @@
</Testables>
</TestAction>
<LaunchAction
buildConfiguration = "Release"
buildConfiguration = "Debug"
selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
enableASanStackUseAfterReturn = "YES"

123
SignalProcessing/BiquadFilter.hpp
View File

@@ -8,6 +8,9 @@
#pragma once
#include <cmath>
#include <numbers>
namespace SignalProcessing {
class BiquadFilter {
@@ -17,6 +20,126 @@ public:
coefficients_[0] = int16_t(1 << 15);
}
enum class Type {
LowPass,
HighPass,
BandPass,
Notch,
AllPass,
Peaking,
LowShelf,
HighShelf
};
BiquadFilter(
const Type type,
const float sample_rate,
const float frequency,
const float resonance,
const float gain,
const bool normalise
) {
const float w0 = 2.0f * std::numbers::pi_v<float> * frequency / sample_rate;
const float alpha = std::sin(w0) / (2.0f * resonance);
const float cos_w0 = std::cos(w0);
float coefficients[5];
float magnitude = 1.0f;
switch(type) {
case Type::LowPass:
coefficients[0] = (1.0f - cos_w0) / 2.0f;
coefficients[1] = 1.0f + cos_w0;
coefficients[2] = (1.0f - cos_w0) / 2.0f;
magnitude = 1.0f + alpha;
coefficients[3] = -2.0f * cos_w0;
coefficients[4] = 1.0f - alpha;
break;
case Type::HighPass:
coefficients[0] = (1.0f - cos_w0) / 2.0f;
coefficients[1] = -(1.0f + cos_w0);
coefficients[2] = (1.0f - cos_w0) / 2.0f;
magnitude = 1.0f + alpha;
coefficients[3] = -2.0f * cos_w0;
coefficients[4] = 1.0f - alpha;
break;
case Type::BandPass:
coefficients[0] = alpha;
coefficients[1] = 0.0f;
coefficients[2] = -alpha;
magnitude = 1.0f + alpha;
coefficients[3] = -2.0f * cos_w0;
coefficients[0] = 1.0f - alpha;
break;
case Type::Notch:
coefficients[0] = 1.0f;
coefficients[1] = -2.0f * cos_w0;
coefficients[2] = 1.0f;
magnitude = 1.0f + alpha;
coefficients[3] = -2.0f * cos_w0;
coefficients[4] = 1.0f - alpha;
break;
case Type::AllPass:
coefficients[0] = 1.0f - alpha;
coefficients[1] = -2.0f * cos_w0;
coefficients[2] = 1.0f + alpha;
magnitude = 1.0f + alpha;
coefficients[3] = -2.0f * cos_w0;
coefficients[4] = 1.0f - alpha;
break;
case Type::Peaking: {
const float a = std::pow(10.0f, gain / 40.0f);
coefficients[0] = 1.0f + (alpha * a);
coefficients[1] = -2.0f * cos_w0;
coefficients[2] = 1.0f - (alpha * a);
magnitude = 1.0f + (alpha / a);
coefficients[3] = -2.0f * cos_w0;
coefficients[4] = 1.0f - (alpha / a);
} break;
case Type::LowShelf: {
const float a_ls = std::pow(10.0f, gain / 40.0f);
const float sqrt_a = std::sqrt(a_ls);
const float alpha_ls =
std::sin(w0) / 2.0f * std::sqrt((a_ls + 1.0f / a_ls) * (1.0f / resonance - 1.0f) + 2.0f);
coefficients[0] = a_ls * ((a_ls + 1.0f) - (a_ls - 1.0f) * cos_w0 + 2.0f * sqrt_a * alpha_ls);
coefficients[1] = 2.0f * a_ls * ((a_ls - 1.0f) - (a_ls + 1.0f) * cos_w0);
coefficients[2] = a_ls * ((a_ls + 1.0f) - (a_ls - 1.0f) * cos_w0 - 2.0f * sqrt_a * alpha_ls);
magnitude = (a_ls + 1.0f) + (a_ls - 1.0f) * cos_w0 + 2.0f * sqrt_a * alpha_ls;
coefficients[3] = -2.0f * ((a_ls - 1) + (a_ls + 1) * cos_w0);
coefficients[4] = (a_ls + 1.0f) + (a_ls - 1.0f) * cos_w0 - 2.0f * sqrt_a * alpha_ls;
} break;
case Type::HighShelf: {
const float a_hs = std::pow(10.0f, gain / 40.0f);
const float sqrt_a_hs = std::sqrt(a_hs);
const float alpha_hs =
std::sin(w0) / 2.0f * std::sqrt((a_hs + 1.0f / a_hs) * (1.0f / resonance - 1.0f) + 2.0f);
coefficients[0] = a_hs * ((a_hs + 1.0f) + (a_hs - 1.0f) * cos_w0 + 2.0f * sqrt_a_hs * alpha_hs);
coefficients[1] = -2.0f * a_hs * ((a_hs - 1.0f) + (a_hs + 1.0f) * cos_w0);
coefficients[2] = a_hs * ((a_hs + 1.0f) + (a_hs - 1.0f) * cos_w0 - 2.0f * sqrt_a_hs * alpha_hs);
magnitude = (a_hs + 1.0f) - (a_hs - 1.0f) * cos_w0 + 2.0f * sqrt_a_hs * alpha_hs;
coefficients[3] = 2.0f * ((a_hs - 1.0f) - (a_hs + 1.0f) * cos_w0);
coefficients[4] = (a_hs + 1.0f) - (a_hs - 1.0f) * cos_w0 - 2.0f * sqrt_a_hs * alpha_hs;
} break;
}
if(normalise) {
for(int c = 0; c < 5; c++) {
coefficients[c] /= magnitude;
}
}
for(int c = 0; c < 5; c++) {
coefficients_[c] = int16_t(coefficients[c] * 32767.0f);
}
}
int16_t apply(const int16_t input) {
const int16_t output = (
coefficients_[0] * input +