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);
}