Instructions
Move the Voice switch on the bottom of the chestplate out of the Demo setting to the first setting spot. Press the Voice button, speak closely into the microphone and say a well-known Darth Vader quote, such as "You don't know the power of the dark side." Determine if that is close enough to the character's voice. To help, the Phrases button can give you a real movie example.
Switch the button to the second setting if the first one doesn't make your voice close enough to Darth Vader's voice. Press the voice button and talk into the microphone to hear what you sound like on this setting. It helps if you deepen your voice as you talk into the microphone and pace your words like Darth Vader.
Change the switch to the third and final setting if the other two aren't enough of a match for your voice. Once again press the Voice button and then talk closely into the microphone.
Press the Breathing button while you speak into the microphone to get the full Darth Vader effect.