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122 lines
4.0 KiB
C++
122 lines
4.0 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2012 maintech GmbH, Otto-Hahn-Str. 15, 97204 Hoechberg, Germany //
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// written by Christian Daniel //
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// //
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// This program is free software; you can redistribute it and/or modify //
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// it under the terms of the GNU General Public License as published by //
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// the Free Software Foundation as version 3 of the License, or //
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// (at your option) any later version. //
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// //
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// This program is distributed in the hope that it will be useful, //
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// but WITHOUT ANY WARRANTY; without even the implied warranty of //
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
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// GNU General Public License V3 for more details. //
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// //
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// You should have received a copy of the GNU General Public License //
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// along with this program. If not, see <http://www.gnu.org/licenses/>. //
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///////////////////////////////////////////////////////////////////////////////////
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#ifndef INCLUDE_FFTWINDOW_H
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#define INCLUDE_FFTWINDOW_H
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#include <vector>
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#include <cmath>
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#include "dsp/dsptypes.h"
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#include "export.h"
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class SDRBASE_API FFTWindow {
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public:
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enum Function {
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Bartlett,
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BlackmanHarris,
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Flattop,
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Hamming,
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Hanning,
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Rectangle,
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Kaiser
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};
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FFTWindow();
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void create(Function function, int n);
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void apply(const std::vector<Real>& in, std::vector<Real>* out);
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void apply(const std::vector<Complex>& in, std::vector<Complex>* out);
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void apply(std::vector<Complex>& in);
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void apply(const Complex* in, Complex* out);
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void apply(Complex* in);
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void setKaiserAlpha(Real alpha); //!< set the Kaiser window alpha factor (default 2.15)
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void setKaiserBeta(Real beta); //!< set the Kaiser window beta factor = pi * alpha
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private:
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std::vector<float> m_window;
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Real m_kaiserAlpha; //!< alpha factor for Kaiser window
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Real m_kaiserI0Alpha; //!< zeroethOrderBessel of alpha above
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static inline Real flatTop(Real n, Real i)
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{
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// correction ?
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return 1.0 - 1.93 * cos((2.0 * M_PI * i) / n) + 1.29 * cos((4.0 * M_PI * i) / n) - 0.388 * cos((6.0 * M_PI * i) / n) + 0.03222 * cos((8.0 * M_PI * i) / n);
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}
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static inline Real bartlett(Real n, Real i)
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{
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// amplitude correction = 2.0
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return (2.0 / (n - 1.0)) * ( (n - 1.0) / 2.0 - fabs(i - (n - 1.0) / 2.0)) * 2.0;
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}
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static inline Real blackmanHarris(Real n, Real i)
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{
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// amplitude correction = 2.79
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return (0.35875 - 0.48829 * cos((2.0 * M_PI * i) / n) + 0.14128 * cos((4.0 * M_PI * i) / n) - 0.01168 * cos((6.0 * M_PI * i) / n)) * 2.79;
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}
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static inline Real hamming(Real n, Real i)
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{
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// amplitude correction = 1.855, energy correction = 1.586
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return (0.54 - 0.46 * cos((2.0 * M_PI * i) / n)) * 1.855;
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}
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static inline Real hanning(Real n, Real i)
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{
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// amplitude correction = 2.0, energy correction = 1.633
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return (0.5 - 0.5 * cos((2.0 * M_PI * i) / n)) * 2.0;
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}
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static inline Real rectangle(Real, Real)
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{
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return 1.0;
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}
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// https://raw.githubusercontent.com/johnglover/simpl/master/src/loris/KaiserWindow.C
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inline Real kaiser(Real n, Real i)
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{
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Real K = ((2.0*i) / n) - 1.0;
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Real arg = sqrt(1.0 - (K*K));
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return zeroethOrderBessel(m_kaiserAlpha*arg) / m_kaiserI0Alpha;
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}
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static inline Real zeroethOrderBessel( Real x )
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{
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const Real eps = 0.000001;
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// initialize the series term for m=0 and the result
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Real besselValue = 0;
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Real term = 1;
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Real m = 0;
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// accumulate terms as long as they are significant
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while(term > eps * besselValue)
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{
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besselValue += term;
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// update the term
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++m;
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term *= (x*x) / (4*m*m);
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}
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return besselValue;
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}
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};
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#endif // INCLUDE_FFTWINDOWS_H
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