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/*
Copyright (C) 2004-2006 Fons Adriaensen
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.
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 for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#ifndef __FILTER1_H
#define __FILTER1_H
/* ---------------------------------------------------------------
Lowpass1
First order lowpass, -3dB at f3dB.
--------------------------------------------------------------- */
class Lowpass1
{
public:
Lowpass1 (void) : _a (0), _z (0) {}
~Lowpass1 (void) {}
void init (float fsam, float f3db);
void reset (void) { _z = 0; }
float process (float x)
{
float d;
d = _a * (x - _z);
x = _z + d;
_z = x + d + 1e-20f;
return x;
}
float _a;
float _z;
};
/* ---------------------------------------------------------------
Allpass1
First order allpass having 0, 90, 180 degrees phase shift at
resp. LF, fmid, HF.
--------------------------------------------------------------- */
class Allpass1
{
public:
Allpass1 (void) : _d (0), _z (0) {}
~Allpass1 (void) {}
void init (float fsam, float fmid);
void reset (void) { _z = 0; }
float process (float x)
{
float y;
x = x - _d * _z;
y = _z + _d * x;
_z = x + 1e-20f;
return y;
}
float _d;
float _z;
};
/* ---------------------------------------------------------------
Pcshelf1
First order shelf filter having the same phase response as a
first order allpass set for 90 degrees at fmid.
Useful for phase aligned shelfs for Ambisonics decoders etc.
See shelf1-plot.cc for tests.
--------------------------------------------------------------- */
class Pcshelf1
{
public:
Pcshelf1 (void) : _d1 (0), _d2 (0), _g (0), _z (0) {}
~Pcshelf1 (void) {}
void init (float fsam, float fmid, float glf, float ghf);
void reset (void) { _z = 0; }
float process (float x)
{
float y;
x = x - _d2 * _z;
y = _z + _d1 * x;
_z = x + 1e-20f;
return _g * y;
}
float _d1;
float _d2;
float _g;
float _z;
};
#endif
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