• Adobe After Effects Expressions

  How to loop a Sin wave within X frames, starting at frame N?

  Posted by Nicolas Hansen on May 29, 2009 at 2:54 am

  Ok so I have a slider that I want to apply a Math.sin() wave to.
  I want the wave to start at Frame 350 and Loop at 275 frames (so the value at Frame 350 is the same at Frame 625)
  It doesn’t matter if the slider value is 0 until frame 350, just as long as frame 350 and 625 are the same, because that span of frames is where I’ll have my loop. (I’d actually prefer if the sin wave started at frame 0 and went on forever)

  Actually, thinking about it now, as long as it loops for 275 frames, it doesn’t matter where it “starts” because by default, frame 350 and 625 will be the same value if it loops every 275 frames

  so having variables like this would be nice:
  loop = 275 // the amount of frames the sine wave takes to loop
  waves = 3 // the number of times the sine wave loops

  maybe even an “offset” variable for the number of frames to offset the sin wave by?

  I’ve been trying to read up on sine and cosine waves, but can’t seem to figure out how to change the duration of the loop
  Any suggestions?
  Thank you!

  Nicolas Hansen replied 16 years, 11 months ago 2 Members · 3 Replies
• 3 Replies

• 

  Nicolas Hansen

  May 29, 2009 at 3:08 am

  edit: nevermind I thought I had it.. it’s late X_X
• 

  Dan Ebberts

  May 29, 2009 at 3:14 am

  I think this does more or less what you want:

  dur = 275;
  startFrame = -75;

  radPerFrame = (Math.PI*2)/dur;
  Math.sin((timeToFrames()+startFrame)*radPerFrame)

  Dan
• 

  Nicolas Hansen

  May 29, 2009 at 3:17 am

  Ah, yes, thank you. I can fiddle with this. Thanks 🙂

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