procedure Filter(cutoff,res:Single);
var   fs, n, x1, x2, c:Integer;
      t, t2, x, scale, f, k, p, e, r, y1, y2, y3, y4, oldx, oldy1, oldy2, oldy3: Single;
      input:Single;
Begin
  fs := EditorSample.Samplerate;
  Editor.GetSelectionS(x1,x2);
  f := (cutoff+cutoff) / fs;
  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);
  y1:=0;
  y2:=0;
  y3:=0;
  y4:=0;
  oldx:=0;
  oldy1:=0;
  oldy2:=0;
  oldy3:=0;
  for n:=x1 to x2 do 
  Begin
	  for c:=0 to EditorSample.NumChans-1 do
    Begin
      input:=EditorSample.GetSampleAt(n,c);
      x := input - 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;
      oldy2 := y2;
      oldy3 := y3;  
      EditorSample.SetSampleAt(n,c,y4);
    End;
  End;
End;

var Form:TScriptDialog;

Begin
Form:=CreateScriptDialog('Lowpass Filter','Simple lowpass filter.');
Form.AddInputKnob('Filter Cutoff',500,1,Round(EditorSample.Samplerate / 2));
Form.AddInputKnob('Filter Resonance',0,0,1);
if Form.Execute then Filter(Form.GetInputValue('Filter Cutoff'),Form.GetInputValue('Filter Resonance'));
Form.Free;
End.