mirror of https://github.com/PCSX2/pcsx2.git
68 lines
1.8 KiB
C++
68 lines
1.8 KiB
C++
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//GiGaHeRz's SPU2 Driver
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//Copyright (c) 2003-2008, David Quintana <gigaherz@gmail.com>
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//
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//This library is free software; you can redistribute it and/or
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//modify it under the terms of the GNU Lesser General Public
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//License as published by the Free Software Foundation; either
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//version 2.1 of the License, or (at your option) any later version.
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//
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//This library is distributed in the hope that it will be useful,
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//but WITHOUT ANY WARRANTY; without even the implied warranty of
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//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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//Lesser General Public License for more details.
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//
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//You should have received a copy of the GNU Lesser General Public
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//License along with this library; if not, write to the Free Software
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//Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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//
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#include "lowpass.h"
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#include <math.h>
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#include <float.h>
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void LPF_init(LPF_data*lpf,double freq, double srate)
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{
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double omega = 2*freq/srate;
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double g = 1.0;
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// calculating coefficients:
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double k,p,q,a;
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double a0,a1,a2,a3,a4;
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k=(4.0*g-3.0)/(g+1.0);
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p=1.0-0.25*k;p*=p;
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// LP:
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a=1.0/(tan(0.5*omega)*(1.0+p));
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p=1.0+a;
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q=1.0-a;
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a0=1.0/(k+p*p*p*p);
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a1=4.0*(k+p*p*p*q);
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a2=6.0*(k+p*p*q*q);
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a3=4.0*(k+p*q*q*q);
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a4= (k+q*q*q*q);
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p=a0*(k+1.0);
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lpf->coef[0]=p;
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lpf->coef[1]=4.0*p;
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lpf->coef[2]=6.0*p;
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lpf->coef[3]=4.0*p;
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lpf->coef[4]=p;
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lpf->coef[5]=-a1*a0;
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lpf->coef[6]=-a2*a0;
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lpf->coef[7]=-a3*a0;
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lpf->coef[8]=-a4*a0;
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}
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double LPF(LPF_data* lpf, double in)
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{
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// per sample:
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double out=lpf->coef[0]*in+lpf->d[0];
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lpf->d[0] =lpf->coef[1]*in+lpf->coef[5]*out+lpf->d[1];
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lpf->d[1] =lpf->coef[2]*in+lpf->coef[6]*out+lpf->d[2];
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lpf->d[2] =lpf->coef[3]*in+lpf->coef[7]*out+lpf->d[3];
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lpf->d[3] =lpf->coef[4]*in+lpf->coef[8]*out;
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return out;
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}
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