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BFM demod: apply de-emphasis

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f4exb
2015-12-08 02:00:30 +01:00
parent 2f8fda7137
commit e533997dbe
6 changed files with 138 additions and 22 deletions
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sdrbase/dsp/filterrc.cpp
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///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2015 F4EXB //
// written by Edouard Griffiths //
// //
// 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 //
// //
// 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/>. //
///////////////////////////////////////////////////////////////////////////////////
#include <QDebug>
#include "dsp/filterrc.h"
// Construct 1st order low-pass IIR filter.
LowPassFilterRC::LowPassFilterRC(Real timeconst) :
m_timeconst(timeconst),
m_y1(0)
{
m_a1 = - exp(-1/m_timeconst);
m_b0 = 1 + m_a1;
}
// Reconfigure
void LowPassFilterRC::configure(Real timeconst)
{
m_timeconst = timeconst;
m_y1 = 0;
m_a1 = - exp(-1/m_timeconst);
m_b0 = 1 + m_a1;
qDebug() << "LowPassFilterRC::configure: t: " << m_timeconst
<< " a1: " << m_a1
<< " b0: " << m_b0;
}
// Process samples.
void LowPassFilterRC::process(const Real& sample_in, Real& sample_out)
{
/*
* Continuous domain:
* H(s) = 1 / (1 - s * timeconst)
*
* Discrete domain:
* H(z) = (1 - exp(-1/timeconst)) / (1 - exp(-1/timeconst) / z)
*/
m_y1 = (sample_in * m_b0) - (m_y1 * m_a1);
sample_out = m_y1;
}