//------------------------------------------------------------------------------
void WahWah::designResonantLowPass(float* dcoefs, float center, float qval)
// design parametric filter based on input center frequency, gain, Q and sampling rate
{
float b0, b1, b2, a0, a1, a2; //storage for continuous-time filter coefs
float acoefs[6];
//Design parametric filter here. Filter should be of the form
//
// 2
// b2s + b1s + b0
// ---------------
// 2
// a2s + a1s + a0
//
// Parameters are center frequency in Hz, gain in dB, and Q.
///////////////START//////////////////
b0 = 1.0; b1 = 0.0; b2 = 0.0;
a0 = 1.0; a1 = 1/(qval*2*pi*center); a2 = 1/(4*pi*pi*center*center);
////////////////END/////////////////////
// pack the analog coeffs into an array and apply the bilinear tranform
acoefs[0] = b0; acoefs[1] = b1; acoefs[2] = b2;
acoefs[3] = a0; acoefs[4] = a1; acoefs[5] = a2;
// inputs the 6 analog coeffs, output the 5 digital coeffs
bilinearTranform(acoefs, dcoefs);
}
//------------------------------------------------------------------------------
void Filters::designParametric(double* dcoefs, double center, double gain, double qval, double fs)
// design parametric filter based on input center frequency, gain, Q and sampling rate
{
double b0, b1, b2, a0, a1, a2; //storage for continuous-time filter coefs
double acoefs[6];
//Design parametric filter here. Filter should be of the form
//
// 2
// b2s + b1s + b0
// ---------------
// 2
// a2s + a1s + a0
//
// Parameters are center frequency in Hz, gain in dB, and Q.
//TODO: design analog filter based on input gain, center frequency and Q
b0 = 1.0; b1 = 0.0; b2 = 0.0;
a0 = 1.0; a1 = 0.0; a2 = 0.0;
///////////////START//////////////////
double Q = qval;
double wc = center*2*M_PI;
// 2nd order butterworth RLP
b2 = 0.0;
b1 = 0.0;
b0 = 1.0;
a2 = 1.0/(wc*wc);
a1 = 1.0/(Q*wc);
a0 = 1.0;
////////////////END/////////////////////
// pack the analog coeffs into an array and apply the bilinear tranform
acoefs[0] = b0; acoefs[1] = b1; acoefs[2] = b2;
acoefs[3] = a0; acoefs[4] = a1; acoefs[5] = a2;
// inputs the 6 analog coeffs, output the 5 digital coeffs
bilinearTranform(acoefs, dcoefs, fs);
}
