pcsx2/plugins/spu2-x/src/Lowpass.cpp

/* SPU2-X, A plugin for Emulating the Sound Processing Unit of the Playstation 2
 * Developed and maintained by the Pcsx2 Development Team.
 *
 * Original portions from SPU2ghz are (c) 2008 by David Quintana [gigaherz]
 *
 * SPU2-X is free software: you can redistribute it and/or modify it under the terms
 * of the GNU Lesser General Public License as published by the Free Software Found-
 * ation, either version 3 of the License, or (at your option) any later version.
 *
 * SPU2-X 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with SPU2-X.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "Global.h"
#include "Lowpass.h"
#include <math.h>
#include <float.h>

template< typename FloatType > __forceinline
LowPassFilter<FloatType>::LowPassFilter( FloatType freq, FloatType srate )
{
	typedef FloatType FT;

	FloatType omega = (FT)2.0 * freq / srate;
	static const FloatType g = (FT)1.0;

	// calculating coefficients:

	FloatType k,p,q,a;
	FloatType a0,a1,a2,a3,a4;

	k = ((FT)4.0*g-(FT)3.0)/(g+(FT)1.0);
	p = (FT)1.0-(FT)0.25*k;
	p *= p;

	// LP:
	a = (FT)1.0/(tan((FT)0.5*omega)*((FT)1.0+p));
	p = (FT)1.0+a;
	q = (FT)1.0-a;

	a0 = (FT)1.0/(k+p*p*p*p);
	a1 = (FT)4.0*(k+p*p*p*q);
	a2 = (FT)6.0*(k+p*p*q*q);
	a3 = (FT)4.0*(k+p*q*q*q);
	a4 =     (k+q*q*q*q);
	p  = a0*(k+(FT)1.0);

	coef[0] = p;
	coef[1] = (FT)4.0*p;
	coef[2] = (FT)6.0*p;
	coef[3] = (FT)4.0*p;
	coef[4] = p;
	coef[5] = -a1*a0;
	coef[6] = -a2*a0;
	coef[7] = -a3*a0;
	coef[8] = -a4*a0;
}

// Processes a single sample into the LPF.
template< typename FloatType > __forceinline
FloatType LowPassFilter<FloatType>::sample( FloatType inval )
{
	const FloatType out = (coef[0]*inval) + d[0];
	d[0] = (coef[1]*inval) + (coef[5]*out) + d[1];
	d[1] = (coef[2]*inval) + (coef[6]*out) + d[2];
	d[2] = (coef[3]*inval) + (coef[7]*out) + d[3];
	d[3] = (coef[4]*inval) + (coef[8]*out);

	return out;
}

LowPassFilter32::LowPassFilter32( float freq, float srate ) :
	impl_lpf( freq, srate )
{
}

LowPassFilter64::LowPassFilter64( double freq, double srate ) :
	impl_lpf( freq, srate )
{
}

float LowPassFilter32::sample( float inval )
{
	return impl_lpf.sample( inval );
}

double LowPassFilter64::sample( double inval )
{
	return impl_lpf.sample( inval );
}