126 lines
3.4 KiB
C++
126 lines
3.4 KiB
C++
/*
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Strawberry Music Player
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This file was part of Clementine.
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Copyright 2004, Melchior FRANZ <mfranz@kde.org>
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Copyright 2010, 2014, John Maguire <john.maguire@gmail.com>
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Copyright 2014, Krzysztof Sobiecki <sobkas@gmail.com>
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Copyright 2017, Santiago Gil
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Strawberry 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, either version 3 of the License, or
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(at your option) any later version.
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Strawberry 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 for more details.
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You should have received a copy of the GNU General Public License
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along with Strawberry. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef FHT_H
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#define FHT_H
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#include <QVector>
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/**
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* Implementation of the Hartley Transform after Bracewell's discrete
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* algorithm. The algorithm is subject to US patent No. 4,646,256 (1987)
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* but was put into public domain by the Board of Trustees of Stanford
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* University in 1994 and is now freely available[1].
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*
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* [1] Computer in Physics, Vol. 9, No. 4, Jul/Aug 1995 pp 373-379
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*/
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class FHT {
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const int num_;
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const int exp2_;
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QVector<float> buf_vector_;
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QVector<float> tab_vector_;
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QVector<int> log_vector_;
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float *buf_();
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float *tab_();
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int *log_();
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/**
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* Create a table of "cas" (cosine and sine) values.
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* Has only to be done in the constructor and saves from
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* calculating the same values over and over while transforming.
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*/
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void makeCasTable();
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/**
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* Recursive in-place Hartley transform. For internal use only!
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*/
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void _transform(float*, int, int);
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public:
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/**
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* Prepare transform for data sets with @f$2^n@f$ numbers, whereby @f$n@f$
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* should be at least 3. Values of more than 3 need a trigonometry table.
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* @see makeCasTable()
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*/
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explicit FHT(uint);
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~FHT();
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int sizeExp() const;
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int size() const;
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void scale(float*, float) const;
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/**
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* Exponentially Weighted Moving Average (EWMA) filter.
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* @param d is the filtered data.
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* @param s is fresh input.
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* @param w is the weighting factor.
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*/
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void ewma(float *d, float *s, float w) const;
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/**
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* Logarithmic audio spectrum. Maps semi-logarithmic spectrum
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* to logarithmic frequency scale, interpolates missing values.
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* A logarithmic index map is calculated at the first run only.
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* @param p is the input array.
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* @param out is the spectrum.
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*/
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void logSpectrum(float *out, float *p);
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/**
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* Semi-logarithmic audio spectrum.
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*/
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void semiLogSpectrum(float*);
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/**
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* Fourier spectrum.
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*/
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void spectrum(float*);
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/**
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* Calculates a mathematically correct FFT power spectrum.
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* If further scaling is applied later, use power2 instead
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* and factor the 0.5 in the final scaling factor.
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* @see FHT::power2()
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*/
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void power(float*);
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/**
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* Calculates an FFT power spectrum with doubled values as a
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* result. The values need to be multiplied by 0.5 to be exact.
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* Note that you only get @f$2^{n-1}@f$ power values for a data set
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* of @f$2^n@f$ input values. This is the fastest transform.
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* @see FHT::power()
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*/
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void power2(float*);
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/**
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* Discrete Hartley transform of data sets with 8 values.
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*/
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static void transform8(float*);
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void transform(float*);
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};
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#endif // FHT_H
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