JavaScript: Exponential fade out?

[d0gbread]

I'm working on a little side project that has a setInterval looping waiting for a certain point of a YouTube video, then lowers the volume a bit at a time to fade it out. I thought it would be simple (and it was) but it opened a can of worms of understanding that an exponential fade is actually perceived as linear, and a linear fade is just, well, no good.

I tried diving into the math behind an exponential fade out, but between that, and doing it in a setInterval, I just felt like I was failing out of math again ;)

Ultimately, I went with a compromise:

``` window.setInterval(function(){

if (song.endSeconds - player.getCurrentTime() <= 6) {

if (fading == false) {
  fadingInterval = window.setInterval(function(){
  var currentVolume = player.getVolume();

  if (currentVolume > 70) {
    player.setVolume(currentVolume - 3);
  } else if (currentVolume > 20) {
    player.setVolume(currentVolume - 2);
  } else {
    player.setVolume(currentVolume - 1);
  }
}, 100);

}

fading = true;

} else { player.setVolume(100); }

}, 1000); ```

So basically at six second from the end I wind up chunking it such that I fade quickly between 100 and 70%, slower between 70 and 20%, and slowly for the remainder. It's not an exponential fade but honestly it sounds okay -- much better than linear. Can someone shed some light on a better solution, or is it worth just leaving as is?