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//////////////////////////////////////////////////////////////////////
// iir.cpp: implementation of the CIir class.
//
// This class implements a biquad IIR filter.
//
// Implements a second order IIR filter stage.
// The transfer function of the filter stage implemented is in
// the direct 2 form :
//
// -1 -2
// B0 + B1 z + B2 z
// H(z) = --------------------
// -1 -2
// 1 + A1 z + A2 z
//
// The block diagram used in the implementation is given below:
//
// input w(n) B0 output
// -----> + ----------+-----[>--> + ----->
// | | |
// | +--+--+ |
// | |Delay| |
// | +--+--+ |
// | -A1 |w(n-1) B1 |
// +----<]-----+-------[>--+
// | | |
// | +--+--+ |
// | |Delay| |
// | +--+--+ |
// | -A2 |w(n-2) B2 |
// +----<]-----+-------[>--+
// w(n) = in - A1*w(n-1) - A2*w(n-2)
// out = B0*w(n) + B1*w(n-1) + B2*w(n-2)
// w(n-2) = w(n-1) w(n-1) = w(n)
//*=========================================================================================
// The filter design equations came from a paper by Robert Bristow-Johnson
// "Cookbook formulae for audio EQ biquad filter coefficients"
//
// History:
// 2011-02-05 Initial creation MSW
// 2011-03-27 Initial release
// 2013-07-28 Added single/double precision math macros
//////////////////////////////////////////////////////////////////////
//==========================================================================================
// + + + This Software is released under the "Simplified BSD License" + + +
//Copyright 2010 Moe Wheatley. All rights reserved.
//
//Redistribution and use in source and binary forms, with or without modification, are
//permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
// conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice, this list
// of conditions and the following disclaimer in the documentation and/or other materials
// provided with the distribution.
//
//THIS SOFTWARE IS PROVIDED BY Moe Wheatley ``AS IS'' AND ANY EXPRESS OR IMPLIED
//WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
//FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL Moe Wheatley OR
//CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
//CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
//SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
//ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
//NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
//ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//The views and conclusions contained in the software and documentation are those of the
//authors and should not be interpreted as representing official policies, either expressed
//or implied, of Moe Wheatley.
//==========================================================================================
#include "iir.h"
/////////////////////////////////////////////////////////////////////////////////
// Construct CIir object
/////////////////////////////////////////////////////////////////////////////////
CIir::CIir()
{
InitBR( 25000, 1000.0, 100000);
}
/////////////////////////////////////////////////////////////////////////////////
// Iniitalize IIR variables for Low Pass IIR filter.
// analog prototype == H(s) = 1 / (s^2 + s/Q + 1)
/////////////////////////////////////////////////////////////////////////////////
void CIir::InitLP( TYPEREAL F0Freq, TYPEREAL FilterQ, TYPEREAL SampleRate)
{
TYPEREAL w0 = K_2PI * F0Freq/SampleRate; //normalized corner frequency
TYPEREAL alpha = MSIN(w0)/(2.0*FilterQ);
TYPEREAL A = 1.0/(1.0 + alpha); //scale everything by 1/A0 for direct form 2
m_B0 = A*( (1.0 - MCOS(w0))/2.0);
m_B1 = A*( 1.0 - MCOS(w0));
m_B2 = A*( (1.0 - MCOS(w0))/2.0);
m_A1 = A*( -2.0*MCOS(w0));
m_A2 = A*( 1.0 - alpha);
m_w1a = 0.0;
m_w2a = 0.0;
m_w1b = 0.0;
m_w2b = 0.0;
}
/////////////////////////////////////////////////////////////////////////////////
// Iniitalize IIR variables for High Pass IIR filter.
// analog prototype == H(s) = s^2 / (s^2 + s/Q + 1)
/////////////////////////////////////////////////////////////////////////////////
void CIir::InitHP( TYPEREAL F0Freq, TYPEREAL FilterQ, TYPEREAL SampleRate)
{
TYPEREAL w0 = K_2PI * F0Freq/SampleRate; //normalized corner frequency
TYPEREAL alpha = MSIN(w0)/(2.0*FilterQ);
TYPEREAL A = 1.0/(1.0 + alpha); //scale everything by 1/A0 for direct form 2
m_B0 = A*( (1.0 + MCOS(w0))/2.0);
m_B1 = -A*( 1.0 + MCOS(w0));
m_B2 = A*( (1.0 + MCOS(w0))/2.0);
m_A1 = A*( -2.0*MCOS(w0));
m_A2 = A*( 1.0 - alpha);
m_w1a = 0.0;
m_w2a = 0.0;
m_w1b = 0.0;
m_w2b = 0.0;
}
/////////////////////////////////////////////////////////////////////////////////
// Iniitalize IIR variables for Band Pass IIR filter.
// analog prototype == H(s) = (s/Q) / (s^2 + s/Q + 1)
/////////////////////////////////////////////////////////////////////////////////
void CIir::InitBP( TYPEREAL F0Freq, TYPEREAL FilterQ, TYPEREAL SampleRate)
{
TYPEREAL w0 = K_2PI * F0Freq/SampleRate; //normalized corner frequency
TYPEREAL alpha = MSIN(w0)/(2.0*FilterQ);
TYPEREAL A = 1.0/(1.0 + alpha); //scale everything by 1/A0 for direct form 2
m_B0 = A * alpha;
m_B1 = 0.0;
m_B2 = A * -alpha;
m_A1 = A*( -2.0*MCOS(w0));
m_A2 = A*( 1.0 - alpha);
m_w1a = 0.0;
m_w2a = 0.0;
m_w1b = 0.0;
m_w2b = 0.0;
}
/////////////////////////////////////////////////////////////////////////////////
// Iniitalize IIR variables for Band Reject(Notch) IIR filter.
// analog prototype == H(s) = (s^2 + 1) / (s^2 + s/Q + 1)
/////////////////////////////////////////////////////////////////////////////////
void CIir::InitBR( TYPEREAL F0Freq, TYPEREAL FilterQ, TYPEREAL SampleRate)
{
TYPEREAL w0 = K_2PI * F0Freq/SampleRate; //normalized corner frequency
TYPEREAL alpha = MSIN(w0)/(2.0*FilterQ);
TYPEREAL A = 1.0/(1.0 + alpha); //scale everything by 1/A0 for direct form 2
m_B0 = A*1.0;
m_B1 = A*( -2.0*MCOS(w0));
m_B2 = A*1.0;
m_A1 = A*( -2.0*MCOS(w0));
m_A2 = A*( 1.0 - alpha);
m_w1a = 0.0;
m_w2a = 0.0;
m_w1b = 0.0;
m_w2b = 0.0;
}
/////////////////////////////////////////////////////////////////////////////////
// Process InLength InBuf[] samples and place in OutBuf[]
//REAL version
/////////////////////////////////////////////////////////////////////////////////
void CIir::ProcessFilter(int InLength, TYPEREAL* InBuf, TYPEREAL* OutBuf)
{
for(int i=0; i<InLength; i++)
{
TYPEREAL w0 = InBuf[i] - m_A1*m_w1a - m_A2*m_w2a;
OutBuf[i] =m_B0*w0 + m_B1*m_w1a + m_B2*m_w2a;
m_w2a = m_w1a;
m_w1a = w0;
}
}
/////////////////////////////////////////////////////////////////////////////////
// Process InLength InBuf[] samples and place in OutBuf[]
//Complex version
/////////////////////////////////////////////////////////////////////////////////
void CIir::ProcessFilter(int InLength, TYPECPX* InBuf, TYPECPX* OutBuf)
{
for(int i=0; i<InLength; i++)
{
TYPEREAL w0a = InBuf[i].re - m_A1*m_w1a - m_A2*m_w2a;
OutBuf[i].re =m_B0*w0a + m_B1*m_w1a + m_B2*m_w2a;
m_w2a = m_w1a;
m_w1a = w0a;
TYPEREAL w0b = InBuf[i].im - m_A1*m_w1b - m_A2*m_w2b;
OutBuf[i].im =m_B0*w0b + m_B1*m_w1b + m_B2*m_w2b;
m_w2b = m_w1b;
m_w1b = w0b;
}
}
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