1 files changed, 42 insertions, 0 deletions
diff --git a/src/biquad.h b/src/biquad.h
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--- /dev/null
+++ b/src/biquad.h
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+#ifndef BIQUAD__H
+#define BIQUAD__H
+#include <complex>
+#include <vector>
+
+// typical usage:
+// biquad butterworth({1., 2., 1.},
+//         {1., -1.99911142347079540116, 0.99911181807963833634});
+
+typedef std::complex<double> C;
+
+class biquad{
+public:
+// d0 must always be 1
+  std::vector<double> c, d;
+  std::vector<C> zeros, poles;
+  double ws1, ws2;      // remembered weighted sums
+
+  C static constexpr C0 = C(0, 0);
+  C static constexpr C1 = C(1, 0);
+// gory-detail constructor
+biquad(std::vector<double> const _c, std::vector<double> const _d,
+                std::vector<C> _zeros, std::vector<C> _poles);
+
+// constructor in terms of coefficients:
+biquad(std::vector<double> const _c, std::vector<double> const _d);
+
+// constructor in terms of zero and pole position,
+// assuming conjugate pairs:
+  biquad(C const zero, C const pole);
+
+// time-domain evaluation:
+  double step(double const Vin);
+
+// z-plane transfer function
+  C xfunc(const C z) const;
+
+  void normalize(C const z = 1);
+  void please_normalize(C const z = 1);
+};
+
+#endif