So here is something that took years to finally figure out because no one teaches this….tuning the doubled vocal less than the main vocal. So obviously you want the main vocal to be pitched very tightly so that the listener isn’t turned off by a sour note here or there. This is a good mindset to have, you should always pitch very tightly while still sounding natural. However with doubled vocals it can be good and sound better to tune them not as perfect. Don’t get me wrong, it still has to be very close to “on pitch” but not pitched as tight as the main because the two vocals will sort of phase out because they are too similar. Also it won’t really give the doubling effect as much and becomes pretty pointless.
A good method to achieve this is to draw with a higher default retune speed setting. This method only works if you are drawing with autotune in graphic mode. When drawing the double vocal’s pitch, go to options and set the default retune speed for the object tool to something higher than what you did for the main vocal. So if you had a default retune speed of 25 when doing the main, try 50 when drawing the doubled vocal.
When using Melodyne or Waves tune you just have to use your ears and move the blobs around without straightening the pitch too much with the pitch modulation tool. Overall it is way easier to not tune the double too tight with these programs because naturally these programs are designed to not tune the vocal very tight leaving it more natural in general. You could always draw the main vocal with Autotune and draw the double with Melodyne. I do this all the time and get superb results!