• Adobe After Effects Expressions

  Random color on audio beat, then hold color til next beat

  Posted by Lionel Vicidomini on February 25, 2013 at 4:02 pm

  Hello everyone,
  I hope the title is self explanatory.
  What I aimed to do is very simple but I’m having a really hard time to do it.
  I have an audio file. I converted it to keyframe. I want to use each beat on the sound to trigger a color change on a layer. This random color stays put until the next beat happens, then it changes and holds this color til the next beat, and so on…

  I know this has to do with the seedRandom as :

  seedRandom(seed, true)
  where seed changes every time x (for example) reaches let’s say 20

  I’m stuck there. I guess it has also to do with if/else statement or a while/do.
  I know this must be extremely simple, but I just don’t get it.

  Thanks for any hint !

  Lionel Vicidomini replied 13 years, 6 months ago 2 Members · 3 Replies
• 3 Replies

• 

  Dan Ebberts

  February 25, 2013 at 6:22 pm

  Don’t feel bad–it’s not extremely simple.

  Try this:

  
threshold = 15.0;

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

  above = false;
  frame = timeToFrames(time);
  while (true){
  t = framesToTime(frame);
  if (above){
  if (audioLev.valueAtTime(t) < threshold){
  frame++;
  break;
  }
  }else if (audioLev.valueAtTime(t) >= threshold){
  above = true;
  }
  if (frame == 0){
  break;
  }
  frame--
  }

  seedRandom(frame,true);
random([0,0,0,1],[1,1,1,1])


  Set threshold to the audio amplitude that signifies a beat.

  Dan
• 

  Lionel Vicidomini

  February 25, 2013 at 6:30 pm

  Perfect ! It works like a charm.
  Ok, now I have to understand it !
  At least I was on the right track 🙂
• 

  Lionel Vicidomini

  February 26, 2013 at 3:09 pm

  I was going to ask a lot of questions about this expression, then I found on your website the template used to do it… with all the explanations I could dreamed of !
  I still struggle a bit with all the “while” statement but I’m starting to get the hang of it.
  So thanks again !

  https://www.motionscript.com/design-guide/audio-trigger.html

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