iir_40.h

// DD4WH LPF DC - 4.0 kHz
// (sampling rate 44.117 kHz)
// 12.2.2016
// Parameters generated using Iowa Hills IIR Filter Designer
// 8th order inv Cheby Lowpass (4-stage cascaded biquad)
// 
// 
//const uint16_t IIR_44_numStages = 6;
// coefficients must be in order: B0, B1, B2, A1, A2
// unlike output by Iowa Hils IIR Filter Designer !

const double IIR_40_Coeffs_0[] =
{   
   0.484810408275220817,
   -0.651221487101388163,
   0.484810408275220817,
   -0.891628778714572134,
   0.210028108163625632
};

const double IIR_40_Coeffs_1[] =
{ 
   0.351872869530550469,
   -0.401617388625892080,
   0.351872869530550469,
   -1.062389411661841750,
   0.364517762097050613
};

const double IIR_40_Coeffs_2[] =
{  
   0.189882490696338585,
   -0.091345663765967006,
   0.189882490696338585,
   -1.306231903874912840,
   0.594651221501622862
};

const double IIR_40_Coeffs_3[] =
{ 
   0.089146208826620985,
   0.118511599523885514,
   0.089146208826620985,
   -1.556718436850091260,
   0.853522454027218824
};

/*
// ELLIPTIC filter coefficients 
// works, but with an unpleasant and annoying hiss sound!

const double IIR_40_Coeffs_0[] =
{   
   0.147439714070734695,
   -0.234713625844170160,
   0.147439714070734695,
   -1.594339282170066820,
   0.654505084467365883
};

const double IIR_40_Coeffs_1[] =
{ 
   0.343454259640266046,
   -0.522129062081838513,
   0.343454259640266046,
   -1.616431618662758530,
   0.781211075861452220
};

const double IIR_40_Coeffs_2[] =
{  
   0.334664568130310369,
   -0.408981103587607198,
   0.334664568130310369,
   -1.640858864246826920,
   0.901206896919840461
};

const double IIR_40_Coeffs_3[] =
{ 
   0.124019274640942659,
   0.058934416406060730,
   0.124019274640942659,
   -1.666344616468945490,
   0.973317582156891459
};
*/