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/***************************************************************************
LowPassFilter.cpp - transmission function of a low pass filter
-------------------
begin : Mar 15 2003
copyright : (C) 2003 by Thomas Eschenbacher
email : Thomas Eschenbacher <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 "LowPassFilter.h"
//***************************************************************************
Kwave::LowPassFilter::LowPassFilter()
:Kwave::SampleSource(nullptr), m_buffer(blockSize()),
m_f_cutoff(M_PI)
{
initFilter();
}
//***************************************************************************
Kwave::LowPassFilter::~LowPassFilter()
{
}
//***************************************************************************
void Kwave::LowPassFilter::goOn()
{
emit output(m_buffer);
}
//***************************************************************************
void Kwave::LowPassFilter::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;
}
//***************************************************************************
/*
* Presence and Shelve filters as given in
* James A. Moorer
* The manifold joys of conformal mapping:
* applications to digital filtering in the studio
* JAES, Vol. 31, No. 11, 1983 November
*/
/*#define SPN MINDOUBLE*/
#define SPN 0.00001
static void shelve(double cf, double boost,
double *a0, double *a1, double *a2,
double *b1, double *b2)
{
double a, A, F, tmp, b0, recipb0, asq, F2, gamma2, siggam2, gam2p1;
double gamman, gammad, ta0, ta1, ta2, tb0, tb1, tb2, aa1, ab1;
a = tan(M_PI * (cf - 0.25));
asq = a * a;
A = pow(10.0, boost / 20.0);
if ((boost < 6.0) && (boost > -6.0)) F = sqrt(A);
else if (A > 1.0) F = A / sqrt(2.0);
else F = A*sqrt(2.0);
F2 = F * F;
tmp = A * A - F2;
if (fabs(tmp) <= SPN) gammad = 1.0;
else gammad = pow((F2 - 1.0) / tmp, 0.25);
gamman = sqrt(A) * gammad;
gamma2 = gamman * gamman;
gam2p1 = 1.0 + gamma2;
siggam2 = 2.0 * sqrt(2.0) / 2.0 * gamman;
ta0 = gam2p1 + siggam2;
ta1 = -2.0 * (1.0 - gamma2);
ta2 = gam2p1 - siggam2;
gamma2 = gammad * gammad;
gam2p1 = 1.0 + gamma2;
siggam2 = 2.0 * sqrt(2.0) / 2.0 * gammad;
tb0 = gam2p1 + siggam2;
tb1 = -2.0 * (1.0 - gamma2);
tb2 = gam2p1 - siggam2;
aa1 = a * ta1;
*a0 = ta0 + aa1 + asq * ta2;
*a1 = 2.0 * a * (ta0 + ta2) + (1.0 + asq) * ta1;
*a2 = asq * ta0 + aa1 + ta2;
ab1 = a * tb1;
b0 = tb0 + ab1 + asq * tb2;
*b1 = 2.0 * a * (tb0 + tb2) + (1.0 + asq) * tb1;
*b2 = asq * tb0 + ab1 + tb2;
recipb0 = 1.0 / b0;
*a0 *= recipb0;
*a1 *= recipb0;
*a2 *= recipb0;
*b1 *= recipb0;
*b2 *= recipb0;
}
//***************************************************************************
void Kwave::LowPassFilter::normed_setfilter_shelvelowpass(double freq)
{
double gain;
double boost = 80.0;
gain = pow(10.0, boost / 20.0);
shelve(freq / (2 * M_PI), boost,
&m_filter.cx, &m_filter.cx1, &m_filter.cx2,
&m_filter.cy1, &m_filter.cy2);
m_filter.cx /= gain;
m_filter.cx1 /= gain;
m_filter.cx2 /= gain;
m_filter.cy1 = -m_filter.cy1;
m_filter.cy2 = -m_filter.cy2;
}
//***************************************************************************
void Kwave::LowPassFilter::input(Kwave::SampleArray data)
{
const Kwave::SampleArray &in = data;
bool ok = m_buffer.resize(in.size());
Q_ASSERT(ok);
Q_UNUSED(ok)
normed_setfilter_shelvelowpass(m_f_cutoff);
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);
}
}
//***************************************************************************
double Kwave::LowPassFilter::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::LowPassFilter::setFrequency(const QVariant fc)
{
double new_freq = QVariant(fc).toDouble();
if (qFuzzyCompare(new_freq, m_f_cutoff)) return; // nothing to do
m_f_cutoff = new_freq;
initFilter();
normed_setfilter_shelvelowpass(m_f_cutoff);
}
//***************************************************************************
//***************************************************************************
#include "moc_LowPassFilter.cpp"
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