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refactor(filter): cache coefficients and extract cutoff calculation

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Add updateCoefficients() that short-circuits when cutoff, resonance,
and type are unchanged. Cache ladderG and formantCoefficients so
processSample() avoids redundant exp()/tan() calls per sample.

Extract static getCutoffHz() from Filter::process() so FilterBank
can compute the keytracked cutoff once per parallel branch instead
of per sample. Simplify formant() and screamer() signatures to use
cached state.
This commit is contained in:
biggy
2026-09-09 14:32:49 +02:00
parent 3b2ecc50f2
commit dc6fd88ed1
3 changed files with 90 additions and 35 deletions
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Source/Filter.h
+8 -2
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@@ -23,9 +23,13 @@ public:
// Single-sample version (used by the comb/naive paths where convenient).
float processSample (float in, float cutoffHz, float res, float drive, int type, int slope) noexcept;
static float getCutoffHz (float cutoffNorm, float keytrack, float noteHz) noexcept;
private:
double sr = 44100.0;
float lastCutoffHz = -1.0f, lastRes = -1.0f;
int lastType = -1;
double ladderG = 0.0;
// TPT SVF state (also reused by formant/screamer).
double ic1eq = 0.0, ic2eq = 0.0;
@@ -42,15 +46,17 @@ private:
// Formant: three parallel bandpass SVFs (state pairs).
std::array<std::array<double, 2>, 3> formantState { { { { 0.0, 0.0 } }, { { 0.0, 0.0 } }, { { 0.0, 0.0 } } } };
std::array<std::array<double, 3>, 3> formantCoefficients {};
void updateCoefficients (float cutoffHz, float res, int type) noexcept;
void updateSvf (double g, double k) noexcept;
double svfLow (double in, double g, double k) noexcept;
double svfBand (double in, double g, double k) noexcept;
double svfHigh (double in, double g, double k) noexcept;
double ladder (double in, double g, double res, double drive, int stages, bool diode) noexcept;
double comb (double in, double freqHz, double res, double drive) noexcept;
double formant (double in, double morph, double res) noexcept;
double screamer (double in, double cutoffHz, double res, double drive) noexcept;
double formant (double in) noexcept;
double screamer (double in, double drive) noexcept;
};
} // namespace serum