pcem/src/filters.h

#define NCoef 2

//fc=350Hz
static inline float low_iir(int i, float NewSample) {
    float ACoef[NCoef+1] = {
        0.00049713569693400649,
        0.00099427139386801299,
        0.00049713569693400649
    };

    float BCoef[NCoef+1] = {
        1.00000000000000000000,
        -1.93522955470669530000,
        0.93726236021404663000
    };

    static float y[2][NCoef+1]; //output samples
    static float x[2][NCoef+1]; //input samples
    int n;

    //shift the old samples
    for(n=NCoef; n>0; n--) {
       x[i][n] = x[i][n-1];
       y[i][n] = y[i][n-1];
    }

    //Calculate the new output
    x[i][0] = NewSample;
    y[i][0] = ACoef[0] * x[i][0];
    for(n=1; n<=NCoef; n++)
        y[i][0] += ACoef[n] * x[i][n] - BCoef[n] * y[i][n];

    return y[i][0];
}

//fc=350Hz
static inline float low_cut_iir(int i, float NewSample) {
    float ACoef[NCoef+1] = {
        0.96839970114733542000,
        -1.93679940229467080000,
        0.96839970114733542000
    };

    float BCoef[NCoef+1] = {
        1.00000000000000000000,
        -1.93522955471202770000,
        0.93726236021916731000
    };

    static float y[2][NCoef+1]; //output samples
    static float x[2][NCoef+1]; //input samples
    int n;

    //shift the old samples
    for(n=NCoef; n>0; n--) {
       x[i][n] = x[i][n-1];
       y[i][n] = y[i][n-1];
    }

    //Calculate the new output
    x[i][0] = NewSample;
    y[i][0] = ACoef[0] * x[i][0];
    for(n=1; n<=NCoef; n++)
        y[i][0] += ACoef[n] * x[i][n] - BCoef[n] * y[i][n];

    return y[i][0];
}

//fc=3.5kHz
static inline float high_iir(int i, float NewSample) {
    float ACoef[NCoef+1] = {
        0.72248704753064896000,
        -1.44497409506129790000,
        0.72248704753064896000
    };

    float BCoef[NCoef+1] = {
        1.00000000000000000000,
        -1.36640781670578510000,
        0.52352474706139873000
    };
    static float y[2][NCoef+1]; //output samples
    static float x[2][NCoef+1]; //input samples
    int n;

    //shift the old samples
    for(n=NCoef; n>0; n--) {
       x[i][n] = x[i][n-1];
       y[i][n] = y[i][n-1];
    }

    //Calculate the new output
    x[i][0] = NewSample;
    y[i][0] = ACoef[0] * x[i][0];
    for(n=1; n<=NCoef; n++)
        y[i][0] += ACoef[n] * x[i][n] - BCoef[n] * y[i][n];

    return y[i][0];
}

//fc=3.5kHz
static inline float high_cut_iir(int i, float NewSample) {
    float ACoef[NCoef+1] = {
        0.03927726802250377400,
        0.07855453604500754700,
        0.03927726802250377400
    };

    float BCoef[NCoef+1] = {
        1.00000000000000000000,
        -1.36640781666419950000,
        0.52352474703279628000
    };
    static float y[2][NCoef+1]; //output samples
    static float x[2][NCoef+1]; //input samples
    int n;

    //shift the old samples
    for(n=NCoef; n>0; n--) {
       x[i][n] = x[i][n-1];
       y[i][n] = y[i][n-1];
    }

    //Calculate the new output
    x[i][0] = NewSample;
    y[i][0] = ACoef[0] * x[i][0];
    for(n=1; n<=NCoef; n++)
        y[i][0] += ACoef[n] * x[i][n] - BCoef[n] * y[i][n];

    return y[i][0];
}


#undef NCoef
#define NCoef 1

//fc=3.2kHz
static inline float sb_iir(int i, float NewSample) {
/*    float ACoef[NCoef+1] = {
        0.03356837051492005100,
        0.06713674102984010200,
        0.03356837051492005100
    };

    float BCoef[NCoef+1] = {
        1.00000000000000000000,
        -1.41898265221812010000,
        0.55326988968868285000
    };*/
    
    float ACoef[NCoef+1] = {
        0.17529642630084405000,
        0.17529642630084405000
    };

    float BCoef[NCoef+1] = {
        1.00000000000000000000,
        -0.64940759319751051000
    };
    static float y[2][NCoef+1]; //output samples
    static float x[2][NCoef+1]; //input samples
    int n;

    //shift the old samples
    for(n=NCoef; n>0; n--) {
       x[i][n] = x[i][n-1];
       y[i][n] = y[i][n-1];
    }

    //Calculate the new output
    x[i][0] = NewSample;
    y[i][0] = ACoef[0] * x[i][0];
    for(n=1; n<=NCoef; n++)
        y[i][0] += ACoef[n] * x[i][n] - BCoef[n] * y[i][n];

    return y[i][0];
}