Perfect LP4 filter

notes
hacked from the exemple of user script in FL Edison
code
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TLP24DB = class
constructor create;
procedure process(inp,Frq,Res:single;SR:integer);
private
t, t2, x, f, k, p, r, y1, y2, y3, y4, oldx, oldy1, oldy2, oldy3: Single;
public outlp:single;
end;
----------------------------------------
implementation

constructor TLP24DB.create;
begin
  y1:=0;
  y2:=0;
  y3:=0;
  y4:=0;
  oldx:=0;
  oldy1:=0;
  oldy2:=0;
  oldy3:=0;
end;
procedure TLP24DB.process(inp: Single; Frq: Single; Res: Single; SR: Integer);
begin
  f := (Frq+Frq) / SR;
  p:=f*(1.8-0.8*f);
  k:=p+p-1.0;
  t:=(1.0-p)*1.386249;
  t2:=12.0+t*t;
  r := res*(t2+6.0*t)/(t2-6.0*t);
  x := inp - r*y4;
  y1:=x*p + oldx*p - k*y1;
  y2:=y1*p+oldy1*p - k*y2;
  y3:=y2*p+oldy2*p - k*y3;
  y4:=y3*p+oldy3*p - k*y4;
  y4 := y4 - ((y4*y4*y4)/6.0);
  oldx := x;
  oldy1 := y1+_kd;
  oldy2 := y2+_kd;;
  oldy3 := y3+_kd;;
  outlp := y4;
end;

// the result is in outlp
// 1/ call MyTLP24DB.Process
// 2/then get the result from outlp.
// this filter have a fantastic sound w/a very special res
// _kd is the denormal killer value.

Comments

This is basically a Moog filter.

Same as http://www.musicdsp.org/showArchiveComment.php?ArchiveID=24
but seems to be in pascal.