//////////// by Nathan Gambles ////////////////////////////////////
sourceAmp = effect("Audio Amplitude Layer")("Layer").effect("Both Channels")("Slider");
// if you use a plugin like Trapcode SoundKeys like that value here.

holdTime = 5
threshold = 15;
audPerc = 70;
fadeInTime = 10;
fadeOutTime =10;

//if using expression controls, uncomment the next lines
//Connecting all the Expression Controls

//holdTime = effect("Padding")("Slider");
//threshold = effect("Threshold")("Slider");
//audPerc = effect("Volume Fade Percent")("Slider");
//fadeInTime = effect("Fade In Frames")("Slider");
//fadeOutTime = effect("Fade Out Frames")("Slider");

function fIn( sAmp, thresh, hT, fiT){             
   nextAud = null;
   myFrame = timeToFrames( );
   while( myFrame <= timeToFrames( ) + hT + fiT ){
      if ( sAmp.valueAtTime( framesToTime( myFrame )) >= thresh){   
         nextAud = myFrame;
         break;
      }else{
         myFrame += 1;
      }
   } 
   if ( nextAud == null ){
      ansI = 0;
   }else{
      ansI = linear( time, framesToTime( nextAud - hT - fiT), framesToTime(nextAud - hT), 0, 100 )
   }
   return ansI; 
}

function fOut( sAmp, thresh, hT, foT ){        
   lastAud = null;
   myFrame = timeToFrames( );
   while( myFrame >= timeToFrames( ) - hT - foT ){
      if ( sAmp.valueAtTime( framesToTime( myFrame )) >= thresh){
         lastAud = myFrame;
         break;
      }else{
         myFrame -= 1;
      }
   }
   if ( lastAud == null ){
      ansOut = 0;
   }else{
      ansOut = linear( time, framesToTime(lastAud + hT), framesToTime( lastAud + hT + foT), 100, 0 )
   }
   return ansOut;
}

//////////////////////////////////////////////

ansO = fOut (sourceAmp, threshold, holdTime, fadeOutTime);
ansI = fIn(sourceAmp, threshold, holdTime, fadeInTime );

percent = Math.max( ansO, ansI ) / 100 ;   

//100 - audPerc * percent + value; // if your intal value is 0%
100 - audPerc * percent // if your intal value is 100%

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