I made this example earlier in the semester after seeing countless projects with the following functionality: turning a sound on when a sensor reading reaches a given level, turning the sound off when a sensor reading falls below a certain level. Most the projects used Minim for sound playback and pause() and play() to start and stop a sound, along with rewind() to send the sound back to the beginning. While this does work, I find a more effective strategy is to fade a sound in and out using shiftGain().

Now this is a fairly simple problem if you can pinpoint the moment a sound should fade in. For example, let’s say you want it to happen when the mouse is clicked.

void mousePressed() {
  player.shiftGain(-80, 13, 1000); 
}

The above line of code will fade the sound over 1,000 milliseconds (i.e. 1 second) from a decibel level of -80 (inaudible) to 13 (some vaguely loud level.)

If you put this code in draw(), however, you’ve got a problem.

void draw() {
  if (sensorVal > threshold) {
    player.shiftGain(-80, 13, 1000); 
  }
}

You can’t call shiftGain() over and over again! You want this to happen just once, the moment the sensor value reaches that threshold. Introducing a boolean is a quick way to solve this problem. If you set the boolean to true when the sound is fading and only call shiftGain() when the boolean is set to false, you’ve now got only one call to the function.

boolean fade = false;

void draw() {
  if (sensorVal > threshold && !fade) {
    player.shiftGain(-80, 13, 1000); 
    fade = true;
  }
}

The question remains: when does fade get set back to false? One likely solution is to reset the boolean when the sensor value falls below the threshold, i.e.

  if (sensorVal > threshold && !fade) {
    player.shiftGain(-80, 13, 1000); 
    fade = true;
  } else if (sensorVal < threshold) {
    fade = false;
  }

Following is an example that does this with a double threshold (fading up above a value and fading down below a value). In addition, it offers some other improvements (such as having the sound fade from its current gain level). The mouseX location is the stand-in for a sensor value.

Source: SoundFade.zip