fftwindow.h

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// Copyright (C) 2012 maintech GmbH, Otto-Hahn-Str. 15, 97204 Hoechberg, Germany //
// written by Christian Daniel                                                   //
//                                                                               //
// This program is free software; you can redistribute it and/or modify          //
// it under the terms of the GNU General Public License as published by          //
// the Free Software Foundation as version 3 of the License, or                  //
// (at your option) any later version.                                           //
//                                                                               //
// This program is distributed in the hope that it will be useful,               //
// but WITHOUT ANY WARRANTY; without even the implied warranty of                //
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                  //
// GNU General Public License V3 for more details.                               //
//                                                                               //
// You should have received a copy of the GNU General Public License             //
// along with this program. If not, see <http://www.gnu.org/licenses/>.          //

#ifndef INCLUDE_FFTWINDOW_H
#define INCLUDE_FFTWINDOW_H

#include <vector>
#define _USE_MATH_DEFINES
#include <math.h>
#include "dsp/dsptypes.h"
#include "export.h"

#undef M_PI
#define M_PI        3.14159265358979323846

class SDRBASE_API FFTWindow {
public:
    enum Function {
        Bartlett,
        BlackmanHarris,
        Flattop,
        Hamming,
        Hanning,
        Rectangle
    };

    void create(Function function, int n);
    void apply(const std::vector<Real>& in, std::vector<Real>* out);
    void apply(const std::vector<Complex>& in, std::vector<Complex>* out);
    void apply(const Complex* in, Complex* out);

private:
    std::vector<float> m_window;

    static inline Real flatTop(Real n, Real i)
    {
        // correction ?
        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);
    }

    static inline Real bartlett(Real n, Real i)
    {
        // amplitude correction = 2.0
        return (2.0 / (n - 1.0)) * ( (n - 1.0) / 2.0 - fabs(i - (n - 1.0) / 2.0)) * 2.0;
    }

    static inline Real blackmanHarris(Real n, Real i)
    {
        // amplitude correction = 2.79
        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;
    }

    static inline Real hamming(Real n, Real i)
    {
        // amplitude correction = 1.855, energy correction = 1.586
        return (0.54 - 0.46 * cos((2.0 * M_PI * i) / n)) * 1.855;
    }

    static inline Real hanning(Real n, Real i)
    {
        // amplitude correction = 2.0, energy correction = 1.633
        return (0.5 - 0.5 * cos((2.0 * M_PI * i) / n)) * 2.0;
    }

    static inline Real rectangle(Real, Real)
    {
        return 1.0;
    }
};

#endif // INCLUDE_FFTWINDOWS_H