• Adobe After Effects Expressions

  How to Modify the “Triggering expression with audio”

  Posted by Darren Caruana on January 29, 2015 at 11:39 am

  Hello I am new to expressions , the motionscript.com site is very helpful , but whenever I try to modify an expression , I get stuck.
  For example I looked for an expression to trigger animations with audio and got this

  threshold = 10.0;

  audioLev = thisComp.layer(“Audio Amplitude”).effect(“Both Channels”)(“Slider”);

  above = false;
  frame = Math.round(time / thisComp.frameDuration);
  while (true){
  t = frame * thisComp.frameDuration;
  if (above){
  if (audioLev.valueAtTime(t) < threshold){
  frame++;
  break;
  }
  }else if (audioLev.valueAtTime(t) >= threshold){
  above = true;
  }
  if (frame == 0){
  break;
  }
  frame–
  }
  if (! above){
  t = 0;
  }else{
  t = time – frame * thisComp.frameDuration;
  }

  amp = 25;
  freq = 5;
  decay = 4.0;

  angle = freq * 2 * Math.PI * t;
  wobble = 1 + amp * Math.sin(angle) / Math.exp(decay * t) / 100;
  [value[0] * wobble, value[1] / wobble]

  But how about if I want to change the wobble expression with something else like a random scale or position ? Meaning that a layer is displayed in a random position triggered with specified audio threshold.
  Sorry If this is a stupid question , I am new and thanks Dan Ebberts for helping people like me.

  For random scale found that this worked perfectly for me ;

  frame = Math.round(time/thisComp.frameDuration);
  seed = Math.floor(frame/15);
  seedRandom(seed,true);
  s = random(50,100);
  [s,s]

  and another one for random position and found this ;

  holdTime = .5; //time to hold each position (seconds)
  minVal = [0.1*thisComp.width, 0.1*thisComp.height];
  maxVal = [0.9*thisComp.width, 0.9*thisComp.height];

  seed = Math.floor(time/holdTime);
  seedRandom(seed,true);
  random(minVal,maxVal)

  Darren Caruana replied 11 years, 6 months ago 1 Member · 0 Replies
• 0 Replies

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