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| double i1, i2, o1, o2; /* temporary variables */
double a0, a1, a2; /* coefficients */
double b0, b1, b2; /* coefficients */
double f; /* last Frequency used */
double q; /* last Q used */
double g; /* last Gain used */
long t; /* last Type used /
static int maxfilterunits=10;
double FilterCell(long Unit, double Input, double Frequency, double Q, double Gain, int Type)
{
/* --------------------------------------------------------------- */
double Output=0,S,omega,A,sn,cs,alpha,beta,temp1,temp2,temp3,temp4;
/* -- check if frequency, Q, gain or type has changed.. and, if so, update coefficients */
if ( ( Frequency != f ) || ( Q != q ) || ( Gain != g ) || ( Type != t ) ) {
f = Frequency; q = Q; g = Gain; t = Type; /* remember last frequency, q, gain and type */
switch (Type) {
case 0: /* no filtering */
b0 = Math.pow( 10.0, Gain / 20.0 ); /* convert from dB to linear */
break;
case 1: /* lowpass */
Gain = Math.pow( 10.0, Gain / 20.0 ); /* convert from dB to linear */
omega = ( Math.PI*2 * Frequency ) / 44100;
sn = Math.sin( omega ); cs = Math.cos( omega );
alpha = sn / ( 2.0 * Q );
a0 = 1.0 / ( 1.0 + alpha );
a1 = ( -2.0 * cs ) * a0;
a2 = ( 1.0 - alpha ) * a0;
b1 = ( 1.0 - cs ) * a0 * Gain;
b0 = b1 * 0.5;
break;
case 2: /* highpass */
Gain = Math.pow( 10.0, Gain / 20.0 ); /* convert from dB to linear */
omega = ( Math.PI*2 * Frequency ) / 44100;
sn = Math.sin( omega ); cs = Math.cos( omega );
alpha = sn / ( 2.0 * Q );
a0 = 1.0 / ( 1.0 + alpha );
a1 = ( -2.0 * cs ) * a0;
a2 = ( 1.0 - alpha ) * a0;
b1 = -( 1.0 + cs ) * a0 * Gain;
b0 = -b1 * 0.5;
break;
case 3: /* bandpass */
Gain = Math.pow( 10.0, Gain / 20.0 ); /* convert from dB to linear */
omega = ( Math.PI*2 * Frequency ) / 44100;
sn =Math.sin( omega ); cs = Math.cos( omega );
alpha = sn / ( 2.0 * Q );
a0 = 1.0 / ( 1.0 + alpha );
a1 = ( -2.0 * cs ) * a0;
a2 = ( 1.0 - alpha ) * a0;
b0 = alpha * a0 * Gain;
break;
case 4: /* notch */
Gain = Math.pow( 10.0, Gain / 20.0 ); /* convert from dB to linear */
omega = ( Math.PI*2 * Frequency ) / 44100;
sn = Math.sin( omega ); cs = Math.cos( omega );
alpha = sn / ( 2.0 * Q );
a0 = 1.0 / ( 1.0 + alpha );
a1 = ( -2.0 * cs ) * a0;
a2 = ( 1.0 - alpha ) * a0;
b0 = a0 * Gain;
b1 = a1 * Gain;
break;
case 5: /* lowshelf */
/* "shelf slope" 1.0 = max slope, because neither Q nor bandwidth is used in */
/* those filters (note: true only for lowshelf and highshelf, not peaking). */
S = 1.0; /* used only by lowshelf and highshelf */
A = Math.pow( 10.0 , ( Gain / 40.0 ) ); /* Gain is expressed in dB */
omega = ( Math.PI*2 * Frequency ) / 44100;
sn = Math.sin( omega ); cs = Math.cos( omega );
temp1 = A + 1.0; temp2 = A - 1.0; temp3 = temp1 * cs; temp4 = temp2 * cs;
beta = sn * Math.sqrt( ( A * A + 1.0 ) / S - temp2 * temp2 );
a0 = 1.0 / ( temp1 + temp4 + beta );
a1 = ( -2.0 * ( temp2 + temp3 ) ) * a0;
a2 = ( temp1 + temp4 - beta ) * a0;
b0 = ( A * ( temp1 - temp4 + beta ) ) * a0;
b1 = ( 2.0 * A * ( temp2 - temp3 ) ) * a0;
b2 = ( A * ( temp1 - temp4 - beta ) ) * a0;
break;
case 6: /* highshelf */
/* "shelf slope" 1.0 = max slope, because neither Q nor bandwidth is used in */
/* those filters (note: true only for lowshelf and highshelf, not peaking). */
S = 1.0; /* used only by lowshelf and highshelf */
A = Math.pow( 10.0, ( Gain / 40.0 ) ); /* Gain is expressed in dB */
omega = ( Math.PI*2 * Frequency ) / 44100;
sn = Math.sin( omega ); cs = Math.cos( omega );
temp1 = A + 1.0; temp2 = A - 1.0; temp3 = temp1 * cs; temp4 = temp2 * cs;
beta = sn * Math.sqrt( ( A * A + 1.0 ) / S - temp2 * temp2 );
a0 = 1.0 / ( temp1 - temp4 + beta );
a1 = ( 2.0 * ( temp2 - temp3 ) ) * a0;
a2 = ( temp1 - temp4 - beta ) * a0;
b0 = ( A * ( temp1 + temp4 + beta ) ) * a0;
b1 = ( -2.0 * A * ( temp2 + temp3 ) ) * a0;
b2 = ( A * ( temp1 + temp4 - beta ) ) * a0;
break;
case 7: /* peaking */
A = Math.pow( 10.0, ( Gain / 40.0 ) ); /* Gain is expressed in dB */
omega = ( Math.PI*2 * Frequency ) / 44100;
sn = Math.sin( omega ); cs = Math.cos( omega );
alpha = sn / ( 2.0 * Q );
temp1 = alpha * A;
temp2 = alpha / A;
a0 = 1.0 / ( 1.0 + temp2 );
a1 = ( -2.0 * cs ) * a0;
a2 = ( 1.0 - temp2 ) * a0;
b0 = ( 1.0 + temp1 ) * a0;
b2 = ( 1.0 - temp1 ) * a0;
break;
}
}
/* -- filter loop: if you don't change the parameters of the filter dynamically, ~only this code will be executed. */
switch (Type) {
case 0: /* no filtering */
Output = b0*Input;
Output = Input;
break;
case 1: /* lowpass */
case 2: /* highpass */
Output = b0*Input + b1*i1 + b0*i2 - a1*o1 - a2*o2;
break;
case 3: /* bandpass */
Output = b0*Input - b0*i2 - a1*o1 - a2*o2;
break;
case 4: /* notch */
Output = b0*Input + b1*i1 + b0*i2 - a1*o1 - a2*o2;
break;
case 5: /* low shelving */
case 6: /* high shelving */
Output = b0*Input + b1*i1 + b2*i2 - a1*o1 - a2*o2;
break;
case 7: /* peaking */
Output = b0*Input + a1*i1 + b2*i2 - a1*o1 - a2*o2;
break;
}
o2=o1; o1=Output; i2=i1; i1=Input; /* update variables for recursion */
return(Output);
} |
