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/***************************************************************************
BandPass.cpp - simple band pass
-------------------
begin : Sun Nov 18 2007
copyright : (C) 2007 by Thomas Eschenbacher
email : Thomas.Eschenbacher@gmx.de
filter functions:
Copyright (C) 1998 Juhana Sadeharju <kouhia@nic.funet.fi>
***************************************************************************/
/***************************************************************************
* *
* 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. *
* *
***************************************************************************/
#include "config.h"
#include <complex>
#include <math.h>
#include "BandPass.h"
//***************************************************************************
Kwave::BandPass::BandPass()
:Kwave::SampleSource(nullptr), m_buffer(blockSize()),
m_frequency(0.5), m_bandwidth(0.1)
{
initFilter();
setfilter_2polebp(m_frequency, m_bandwidth);
}
//***************************************************************************
Kwave::BandPass::~BandPass()
{
}
//***************************************************************************
void Kwave::BandPass::goOn()
{
emit output(m_buffer);
}
//***************************************************************************
double Kwave::BandPass::at(double f)
{
/*
* filter function as extracted from the aRts code:
*
* y[t] = cx*x[t] + cx1*x[t-1] + cx2*x[t-2]
* + cy1*y[t-1] + cy2*y[t-2];
*
* convert filter coefficients to our notation:
*/
double a0, a1, a2, b1, b2;
a0 = m_filter.cx;
a1 = m_filter.cx1;
a2 = m_filter.cx2;
b1 = m_filter.cy1;
b2 = m_filter.cy2;
/*
* a0*z^2 + a1*z + a2
* H(z) = ------------------ | z = e ^ (j*2*pi*f)
* z^2 - b1*z - b0
*/
std::complex<double> h;
std::complex<double> w;
std::complex<double> j(0.0,1.0);
std::complex<double> z;
w = f;
z = std::exp(j*w);
// get h[z] at z=e^jw
h = 0.95 * (a0 * (z*z) + (a1*z) + a2) / ((z*z) - (b1*z) - b2);
return sqrt(std::norm(h));
}
//***************************************************************************
void Kwave::BandPass::initFilter()
{
m_filter.x1 = 0.0;
m_filter.x2 = 0.0;
m_filter.y1 = 0.0;
m_filter.y2 = 0.0;
m_filter.y = 0.0;
}
//***************************************************************************
/*
* As in ''An introduction to digital filter theory'' by Julius O. Smith
* and in Moore's book; I use the normalized version in Moore's book.
*/
void Kwave::BandPass::setfilter_2polebp(double freq, double R)
{
m_filter.cx = 1.0 - R;
m_filter.cx1 = 0.0;
m_filter.cx2 = - (1.0 - R) * R;
m_filter.cy1 = 2.0 * R * cos(freq);
m_filter.cy2 = -R * R;
}
//***************************************************************************
void Kwave::BandPass::input(Kwave::SampleArray data)
{
const Kwave::SampleArray &in = data;
bool ok = m_buffer.resize(in.size());
Q_ASSERT(ok);
Q_UNUSED(ok)
setfilter_2polebp(m_frequency, m_bandwidth);
Q_ASSERT(in.size() == m_buffer.size());
for (unsigned i = 0; i < in.size(); ++i)
{
// do the filtering
m_filter.x = sample2double(in[i]);
m_filter.y =
m_filter.cx * m_filter.x +
m_filter.cx1 * m_filter.x1 +
m_filter.cx2 * m_filter.x2 +
m_filter.cy1 * m_filter.y1 +
m_filter.cy2 * m_filter.y2;
m_filter.x2 = m_filter.x1;
m_filter.x1 = m_filter.x;
m_filter.y2 = m_filter.y1;
m_filter.y1 = m_filter.y;
m_buffer[i] = double2sample(0.95 * m_filter.y);
}
}
//***************************************************************************
void Kwave::BandPass::setFrequency(const QVariant fc)
{
double new_freq = QVariant(fc).toDouble();
if (qFuzzyCompare(new_freq, m_frequency)) return; // nothing to do
m_frequency = new_freq;
initFilter();
setfilter_2polebp(m_frequency, m_bandwidth);
}
//***************************************************************************
void Kwave::BandPass::setBandwidth(const QVariant bw)
{
double new_bw = QVariant(bw).toDouble();
if (qFuzzyCompare(new_bw, m_bandwidth)) return; // nothing to do
m_bandwidth = new_bw;
initFilter();
setfilter_2polebp(m_frequency, m_bandwidth);
}
//***************************************************************************
//***************************************************************************
#include "moc_BandPass.cpp"
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