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59 lines
2.1 KiB
C++
59 lines
2.1 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2015 F4EXB //
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// written by Edouard Griffiths //
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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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// //
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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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#include <QDebug>
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#include "dsp/filterrc.h"
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// Construct 1st order low-pass IIR filter.
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LowPassFilterRC::LowPassFilterRC(Real timeconst) :
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m_timeconst(timeconst),
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m_y1(0)
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{
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m_a1 = - exp(-1/m_timeconst);
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m_b0 = 1 + m_a1;
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}
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// Reconfigure
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void LowPassFilterRC::configure(Real timeconst)
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{
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m_timeconst = timeconst;
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m_y1 = 0;
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m_a1 = - exp(-1/m_timeconst);
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m_b0 = 1 + m_a1;
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qDebug() << "LowPassFilterRC::configure: t: " << m_timeconst
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<< " a1: " << m_a1
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<< " b0: " << m_b0;
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}
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// Process samples.
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void LowPassFilterRC::process(const Real& sample_in, Real& sample_out)
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{
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/*
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* Continuous domain:
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* H(s) = 1 / (1 - s * timeconst)
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*
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* Discrete domain:
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* H(z) = (1 - exp(-1/timeconst)) / (1 - exp(-1/timeconst) / z)
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*/
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m_y1 = (sample_in * m_b0) - (m_y1 * m_a1);
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sample_out = m_y1;
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}
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