slider1:50<0,100,0.01>Frequency (Scale)
slider2:0.707<0.2,4,0.001>Bandwidth
slider3:0<-12,12,0.1>Gain (dB)
slider4:6<0,8,1{lpf (bw),hpf (bw),bpf (constant skirt gain) (bw),bpf2 (constant peak gain) (bw),notch (bw),all pass (bw),peak (bw;dB),lsf (bw;dB),hsf (bw;dB)}>Filter type
slider5:0<-24,24,0.1>Output (dB)

in_pin:L in
in_pin:R in
out_pin:L out
out_pin:R out

@slider
// frequency slider scaling
tmpx = 16+slider1*1.20103;
tmpy = floor(exp(tmpx*log(1.059))*8.17742);

	// filter calculation
omega = 2*$pi*tmpy/srate;
slider4 < 8 ? (
K = tan(omega/2);
):(
K = tan(($pi-omega)/2); //HSF only
);
Q = max(min(slider2,4),0.2);
V = 10^(-slider3/20);

outvol = 10^(slider5/20);

slider4==0?(
//LPF:
b0 = K^2;
b1 = 2*K^2;
b2 = K^2;
a0 = 1 + K/Q + K^2;
a1 = 2*(K^2 - 1);
a2 = 1 - K/Q + K^2;
);

slider4==1?(
//HPF:
b0 = 1;
b1 = -2;
b2 = 1;
a0 = 1 + K/Q + K^2;
a1 = 2*(K^2 - 1);
a2 = 1 - K/Q + K^2;
);

slider4==2?(
//BPF:
b0 = K;
b1 = 0;
b2 = -K;
a0 = 1 + K/Q + K^2;
a1 = 2*(K^2 - 1);
a2 = 1 - K/Q + K^2;
);

slider4==3?(
//BPF2:
b0 = K/Q;
b1 = 0;
b2 = -K/Q;
a0 = 1 + K/Q + K^2;
a1 = 2*(K^2 - 1);
a2 = 1 - K/Q + K^2;
);

slider4==4?(
//NOTCH:
b0 = 1 + K^2;
b1 = 2*(K^2 - 1);
b2 = 1 + K^2;
a0 = 1 + K/Q + K^2;
a1 = 2*(K^2 - 1);
a2 = 1 - K/Q + K^2;
);

slider4==5?(
//ALL-PASS:
b0 = 1 - K/Q + K^2;
b1 = 2*(K^2 - 1);
b2 = 1 + K/Q + K^2;
a0 = 1 + K/Q + K^2;
a1 = 2*(K^2 - 1);
a2 = 1 - K/Q + K^2;
);

slider4==6?(
//PEQ:
//boost:
b0 = 1 + V*K/Q + K^2;
b1 = 2*(K^2 - 1);
b2 = 1 - V*K/Q + K^2;
a0 = 1 + K/Q + K^2;
a1 = 2*(K^2 - 1);
a2 = 1 - K/Q + K^2;

//cut:
b0 = 1 + K/Q + K^2;
b1 = 2*(K^2 - 1);
b2 = 1 - K/Q + K^2;
a0 = 1 + V*K/Q + K^2;
a1 = 2*(K^2 - 1);
a2 = 1 - V*K/Q + K^2;
);

slider4==7?(
//LSH:
//boost:
b0 = 1 + sqrt(V)*K/Q + V*K^2;
b1 = 2*(V*K^2 - 1);
b2 = 1 - sqrt(V)*K/Q + V*K^2;
a0 = 1 + K/Q + K^2;
a1 = 2*(K^2 - 1);
a2 = 1 - K/Q + K^2;

//cut:
b0 = 1 + K/Q + K^2;
b1 = 2*(K^2 - 1);
b2 = 1 - K/Q + K^2;
a0 = 1 + sqrt(V)*K/Q + V*K^2;
a1 = 2*(V*K^2 - 1);
a2 = 1 - sqrt(V)*K/Q + V*K^2;
);

slider4==8?(
//HSH:
//boost:
b0 = 1 + sqrt(V)*K/Q + V*K^2;
b1 = -2*(V*K^2 - 1);
b1 = 1 - sqrt(V)*K/Q + V*K^2;
a0 = 1 + K/Q + K^2;
a1 = -2*(K^2 - 1);
a2 = 1 - K/Q + K^2;

//cut:
b0 = 1 + K/Q + K^2;
b1 = -2*(K^2 - 1);
b2 = 1 - K/Q + K^2;
a0 = 1 + sqrt(V)*K/Q + V*K^2;
a1 = -2*(V*K^2 - 1);
a2 = 1 - sqrt(V)*K/Q + V*K^2;
);

a1 /= a0;
a2 /= a0;
b0 /= a0;
b1 /= a0;
b2 /= a0;

@sample
inA = spl0;
inB = spl1;

//Left
x2A = x1A;
x1A = x0A;
x0A = inA;

y2A = y1A;
y1A = y0A;
y0A = b0*x0A + b1*x1A + b2*x2A - a1*y1A - a2*y2A;

//Right
x2B = x1B;
x1B = x0B;
x0B = inB;

y2B = y1B;
y1B = y0B;
y0B = b0*x0B + b1*x1B + b2*x2B - a1*y1B - a2*y2B;

//Output
spl0 = y0A;
spl1 = y0B;

spl0 *= outvol;
spl1 *= outvol;

@gfx 0 26
gfx_x=gfx_y=10;
gfx_r=gfx_b=0;gfx_g=gfx_a=1;
gfx_drawchar($'F');
gfx_drawchar($' ');
gfx_drawchar($'=');
gfx_drawchar($' ');
gfx_drawnumber(tmpy,0);
gfx_drawchar($' ');
gfx_drawchar($'H');
gfx_drawchar($'z');
