X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=filter.cpp;fp=filter.cpp;h=d8f97010f2670dd2f4566fa5153f01223640672f;hb=cec99d15ad920457eea61bc442b5ba610c13430e;hp=0000000000000000000000000000000000000000;hpb=1d431da4497326b4496cdc6596c52736d98699e7;p=c64tapwav

diff --git a/filter.cpp b/filter.cpp
new file mode 100644
index 0000000..d8f9701
--- /dev/null
+++ b/filter.cpp
@@ -0,0 +1,25 @@
+#include <math.h>
+
+#include "filter.h"
+
+void Filter::reset()
+{
+	d0 = d1 = 0.0f;
+}
+
+Filter Filter::lpf(float cutoff_radians)
+{
+	float resonance = 1.0f / sqrt(2.0f);
+	float sn = sin(cutoff_radians), cs = cos(cutoff_radians);
+	float alpha = float(sn / (2 * resonance));
+
+	// coefficients for lowpass filter
+        float a0 = 1 + alpha;
+	float b0 = (1 - cs) * 0.5f;
+	float b1 = 1 - cs;
+	float b2 = b0;
+        float a1 = -2 * cs;
+        float a2 = 1 - alpha;
+
+	return Filter(a0, a1, a2, b0, b1, b2);
+}