resampler: add HyperbolicCosineWindow
Much cleaner spectrograms.
diff --git a/src/flowgraph/resampler/KaiserWindow.h b/src/flowgraph/resampler/KaiserWindow.h
index 6a5d086..f45aced 100644
--- a/src/flowgraph/resampler/KaiserWindow.h
+++ b/src/flowgraph/resampler/KaiserWindow.h
@@ -19,17 +19,21 @@
#include "Math.h"
+namespace resampler {
+
+
/**
* Calculate a Kaiser window centered at 0.
*/
class KaiserWindow {
public:
KaiserWindow() {
- setStopBandAttenuation(90);
+ setStopBandAttenuation(60);
}
/**
* @param attenuation typical values range from 30 to 90 dB
+ * @return beta
*/
double setStopBandAttenuation(double attenuation) {
double beta = 0.0;
@@ -45,15 +49,30 @@
void setBeta(double beta) {
mBeta = beta;
- mInverseBesselBeta = 1.0 / Math::bessel(beta);
+ mInverseBesselBeta = 1.0 / bessel(beta);
}
/**
* @param x ranges from -1.0 to +1.0
*/
double operator()(double x) {
- double w = mBeta * sqrt(1.0 - (x * x));
- return Math::bessel(w) * mInverseBesselBeta;
+ double x2 = x * x;
+ if (x2 >= 1.0) return 0.0;
+ double w = mBeta * sqrt(1.0 - x2);
+ return bessel(w) * mInverseBesselBeta;
+ }
+
+ static double bessel(double x) {
+ double y = cosh(0.970941817426052 * x);
+ y += cosh(0.8854560256532099 * x);
+ y += cosh(0.7485107481711011 * x);
+ y += cosh(0.5680647467311558 * x);
+ y += cosh(0.3546048870425356 * x);
+ y += cosh(0.120536680255323 * x);
+ y *= 2;
+ y += cosh(x);
+ y /= 13;
+ return y;
}
private:
@@ -61,4 +80,5 @@
double mInverseBesselBeta = 1.0;
};
+} // namespace resampler
#endif //RESAMPLER_KAISER_WINDOW_H
