fft.cc

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/*
    Copyright (C) 2008 Paul Davis
    Author: Sampo Savolainen

    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; either version 2 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 for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

*/
#include "fft.h"

#include <stdlib.h>
#include <string.h>
#include <math.h>

using namespace GTKArdour;

FFT::FFT(uint32_t windowSize)
        : _window_size(windowSize),
          _data_size(_window_size/2),
        _iterations(0),
        _hann_window(0)
{
        _fftInput  = (float *) fftwf_malloc(sizeof(float) * _window_size);

        _fftOutput = (float *) fftwf_malloc(sizeof(float) * _window_size);

        _power_at_bin  = (float *) malloc(sizeof(float) * _data_size);
        _phase_at_bin  = (float *) malloc(sizeof(float) * _data_size);

        _plan = fftwf_plan_r2r_1d(_window_size, _fftInput, _fftOutput, FFTW_R2HC, FFTW_ESTIMATE);

        reset();
}

void
FFT::reset()
{
        memset(_power_at_bin, 0, sizeof(float) * _data_size);
        memset(_phase_at_bin, 0, sizeof(float) * _data_size);

        _iterations = 0;
}

void
FFT::analyze(ARDOUR::Sample *input, WindowingType windowing_type)
{
        _iterations++;

        memcpy(_fftInput, input, sizeof(float) * _window_size);

        if (windowing_type == HANN) {
                float *window = get_hann_window();
                for (uint32_t i = 0; i < _window_size; i++) {
                        _fftInput[i] *= window[i];
                }
        }

        fftwf_execute(_plan);

        _power_at_bin[0] += _fftOutput[0] * _fftOutput[0];
        _phase_at_bin[0] += 0.0;

        float power;
        float phase;

#define Re (_fftOutput[i])
#define Im (_fftOutput[_window_size-i])
        for (uint32_t i=1; i < _data_size - 1; i++) {

                power = (Re * Re) + (Im * Im);
                phase = atanf(Im / Re);

                if (Re < 0.0 && Im > 0.0) {
                        phase += M_PI;
                } else if (Re < 0.0 && Im < 0.0) {
                        phase -= M_PI;
                }

                _power_at_bin[i] += power;
                _phase_at_bin[i] += phase;
        }
#undef Re
#undef Im
}

void
FFT::calculate()
{
        if (_iterations > 1) {
                for (uint32_t i=0; i < _data_size - 1; i++) {
                        _power_at_bin[i] /= (float)_iterations;
                        _phase_at_bin[i] /= (float)_iterations;
                }
                _iterations = 1;
        }
}

float *
FFT::get_hann_window()
{
        if (_hann_window)
                return _hann_window;


        _hann_window = (float *) malloc(sizeof(float) * _window_size);

        double sum = 0.0;

        for (uint32_t i=0; i < _window_size; i++) {
                _hann_window[i]=0.81f * ( 0.5f - (0.5f * (float) cos(2.0f * M_PI * (float)i / (float)(_window_size))));
                sum += _hann_window[i];
        }

        double isum = 1.0 / sum;

        for (uint32_t i=0; i < _window_size; i++) {
                _hann_window[i] *= isum;
        }

        return _hann_window;
}


FFT::~FFT()
{
        if (_hann_window) {
                free(_hann_window);
        }
        fftwf_destroy_plan(_plan);
        free(_power_at_bin);
        free(_phase_at_bin);
        free(_fftOutput);
        free(_fftInput);
}