• Adobe After Effects Expressions

  Why multiply on Pi

  Posted by Serge Druz on March 24, 2021 at 12:18 pm

  Hi, everybody, I noticed some pro artists do multiplication on Pi. Can you, please, explain what sense in that?
  For example in this expression, which gives you scale hesitation on each marker.

  look at “angle” variable, expression will work without “Math.PI” as well.

  n = 0;

  t = 0;

  if (marker.numKeys > 0){

  n = marker.nearestKey(time).index;

  if (marker.key(n).time > time) n–;

  }

  if (n > 0) t = time – marker.key(n).time;

  amp = 15;

  freq = 5;

  decay = 3.0;

  angle = freq * 2 * Math.PI * t;

  scaleFact = (100 + amp * Math.sin(angle) / Math.exp(decay * t)) / 100;

  [value[0] * scaleFact, value[1] / scaleFact];

  Serge Druz replied 5 years, 6 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  March 24, 2021 at 12:54 pm

  Multiplying by 2*pi allows you to express your frequency (freq) in cycles per second. So in your expression, the damped sine wave will oscillate at 5 cycles per second. Without the 2*pi, it will still oscillate, just a frequency that’s harder to predict. It’s just convenience (and convention) mainly.
• 

  Serge Druz

  March 25, 2021 at 1:12 pm

  God, bless internet, Dan, thank you so much for explaining things, really appreciate this.

Reply to this Discussion! Login or Sign Up