Have you heard the growl function in Vocaloid 4 and would like to use it--but you only have Vocaloid 3? Well, you can kind of emulate that by using VST plugins! Using an overdrive or tube amp simulation plugin can give vocals a bit of grit and gruffness to emulate singers with throaty vocals, like Joan Jett or Courtney Love.
I like to use Bitcrusher, which comes with Presonus Studio One Artist. There are many free "Bitcrusher" VST plugins around, but they all are a little different and sound a little different, so don't be afraid to test them out if you want to use a Bitcrusher type plugin.
The key is to apply just a light touch just to give the vocals some edge. You'll also notice that it makes the singer sound like she is singing into a live mic on stage.
Using the VST plugin in a DAW rather than in the Vocaloid editor gives the advantage of being able to use automation to control where, when, and how much of the effect to apply to the vocals.
Below is a video with an example of Gumi singing the opening verse from Hole's Celebrity Skin. What do you think? Do you think the growl function in Vocaloid 4 sounds better?