6502/CLK
1
0
Fork 0
mirror of https://github.com/TomHarte/CLK.git synced 2026-01-26 21:16:19 +00:00
Code Issues Projects Releases Wiki Activity

Attempt further to improve filter precision.

Browse Source
This commit is contained in:
Thomas Harte
2025-11-13 11:54:37 -05:00
parent d00546dd77
commit 86bf019aac
2 changed files with 30 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
Components/SID/SID.cpp
View File

@@ -112,7 +112,7 @@ void SID::update_filter() {
type,
1'000'000.0f,
30.0f + float(filter_cutoff_.get()) * 5.8f,
0.707f + float(filter_resonance_.get()) * 0.25f,
0.707f + float(filter_resonance_.get()) * 0.125f,
6.0f,
true
);

35
SignalProcessing/BiquadFilter.hpp
View File

@@ -134,19 +134,32 @@ public:
}
}
for(int c = 0; c < 5; c++) {
assert(std::abs(coefficients[c]) < 32768.0f / 16384.0f);
coefficients_[c] = int16_t(coefficients[c] * 16384.0f);
#ifdef FIXED
coefficients_[c] = FixedType(coefficients[c] * FixedMultiplier);
#else
coefficients_[c] = coefficients[c];
#endif
}
}
int16_t apply(const int16_t input) {
const int16_t output = (
#ifdef FIXED
const auto applied =
coefficients_[0] * input +
coefficients_[1] * inputs_[0] +
coefficients_[2] * inputs_[1] -
coefficients_[3] * outputs_[0] -
coefficients_[4] * outputs_[1]
) >> 14;
coefficients_[4] * outputs_[1];
const auto output = int16_t(applied >> FixedShift);
#else
const float output =
coefficients_[0] * float(input) +
coefficients_[1] * inputs_[0] +
coefficients_[2] * inputs_[1] -
coefficients_[3] * outputs_[0] -
coefficients_[4] * outputs_[1];
#endif
inputs_[1] = inputs_[0];
inputs_[0] = input;
@@ -157,9 +170,19 @@ public:
}
private:
#ifdef FIXED
int16_t inputs_[2]{};
int16_t outputs_[2]{};
int16_t coefficients_[5]{};
using FixedType = int64_t;
static constexpr int FixedShift = 48;
static constexpr auto FixedMultiplier = static_cast<float>(int64_t(1) << FixedShift);
FixedType coefficients_[5]{};
#else
float inputs_[2]{};
float outputs_[2]{};
float coefficients_[5]{};
#endif
// 0 = b0; 1 = b1; 2 = b2; 3 = a1; 4 = a2
};