Automatic Vocal Doubler A plugin for creating realistic vocal doubling easily and quickly. Duo allows you to freely adjust the pitch, timing, and vibrato depth, as well as the timbre of the vocals themselves. This makes it possible to create double tracks that sound just like the lead vocal, or even completely different backing vocals. You can also individually control the levels and panning of the original and doubled voices, making it ideal for adding depth to vocals or creating impact in the overall song.