fft_helpers.h

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/*
 * fft_helpers.h - some functions around FFT analysis
 *
 * Copyright (c) 2008-2012 Tobias Doerffel <tobydox/at/users.sourceforge.net>
 * Copyright (c) 2019 Martin Pavelek <he29.HS/at/gmail.com>
 *
 * This file is part of LMMS - https://lmms.io
 *
 * 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 (see COPYING); if not, write to the
 * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301 USA.
 *
 */
 
#ifndef LMMS_FFT_HELPERS_H
#define LMMS_FFT_HELPERS_H
 
#include "lmms_export.h"
 
#include <vector>
#include <fftw3.h>
 
namespace lmms
{
 
// NOTE: FFT_BUFFER_SIZE should be considered deprecated!
// It is used by Eq plugin and some older code here, but this should be a user
// switchable parameter, not a constant. Use a value from FFT_BLOCK_SIZES
constexpr auto FFT_BUFFER_SIZE = std::size_t{2048};
 
// Allowed FFT block sizes. Ranging from barely useful to barely acceptable
// because of performance and latency reasons.
const std::vector<unsigned int> FFT_BLOCK_SIZES = {256, 512, 1024, 2048, 4096, 8192, 16384};
 
// List of FFT window functions supported by precomputeWindow()
enum class FFTWindow
{
        Rectangular = 0,
        BlackmanHarris,
        Hamming,
        Hanning
};
 

float LMMS_EXPORT maximum(const float *abs_spectrum, unsigned int spec_size);
float LMMS_EXPORT maximum(const std::vector<float> &abs_spectrum);
 

int LMMS_EXPORT normalize(const float *abs_spectrum, float *norm_spectrum, unsigned int bin_count, unsigned int block_size);
int LMMS_EXPORT normalize(const std::vector<float> &abs_spectrum, std::vector<float> &norm_spectrum, unsigned int block_size);
 

int LMMS_EXPORT notEmpty(const std::vector<float> &spectrum);
 

int LMMS_EXPORT precomputeWindow(float *window, unsigned int length, FFTWindow type, bool normalized = true);
 

int LMMS_EXPORT absspec(const fftwf_complex *complex_buffer, float *absspec_buffer,
                                                unsigned int compl_length);
 

int LMMS_EXPORT compressbands(const float * _absspec_buffer, float * _compressedband,
                        int _num_old, int _num_new, int _bottom, int _top);
 
 
} // namespace lmms
 
#endif // LMMS_FFT_HELPERS_H