musicdsp.org source code archive - WSInf

Fast LFO in Delphi... (click this to go back to the index)
References : Posted by Dambrin Didier ( gol [AT] e-officedirect [DOT] com )
Linked file : LFOGenerator.zip
Notes :
[from Didier's mail...]
[see attached zip file too!]
I was working on a flanger, & needed an LFO for it. I first used a Sin(), but it was too slow, then tried a big wavetable, but it wasn't accurate
enough.
I then checked the alternate sine generators from your web site, & while they're good, they all can drift, so you're also wasting too much CPU in
branching for the drift checks.
So I made a quick & easy linear LFO, then a sine-like version of it. Can be useful for LFO's, not to output as sound.
If has no branching & is rather simple. 2 Abs() but apparently they're fast. In all cases faster than a Sin()
It's in delphi, but if you understand it you can translate it if you want.
It uses a 32bit integer counter that overflows, & a power for the sine output.
If you don't know delphi, $ is for hex (h at the end in c++?), Single is 32bit float, integer is 32bit integer (signed, normally).
Code :
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls, ExtCtrls, ComCtrls;
type
TForm1 = class(TForm)
PaintBox1: TPaintBox;
Bevel1: TBevel;
procedure PaintBox1Paint(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.PaintBox1Paint(Sender: TObject);
var n,Pos,Speed:Integer;
Output,Scale,HalfScale,PosMul:Single;
OurSpeed,OurScale:Single;
begin
OurSpeed:=100; // 100 samples per cycle
OurScale:=100; // output in -100..100
Pos:=0; // position in our linear LFO
Speed:=Round($100000000/OurSpeed);
// --- triangle LFO ---
Scale:=OurScale*2;
PosMul:=Scale/$80000000;
// loop
for n:=0 to 299 do
Begin
// inc our 32bit integer LFO pos & let it overflow. It will be seen as signed when read by the math unit
Pos:=Pos+Speed;
Output:=Abs(Pos*PosMul)-OurScale;
// visual
Paintbox1.Canvas.Pixels[n,Round(100+Output)]:=clRed;
End;
// --- sine-like LFO ---
Scale:=Sqrt(OurScale*4);
PosMul:=Scale/$80000000;
HalfScale:=Scale/2;
// loop
for n:=0 to 299 do
Begin