2 different types of vocal can be achieved here: first is a straight double, either mono or stereo, offset in either timing and/or pitch. The second is to create an harmony with your existing vocal; this can be done from a single source or by locking together multiple sources. The video above has each type, as well as original for comparison purposes.
The double or harmony will be delivered back as a single file for you to mix into your existing vocal however you wish.
Delivered files are 24bit/44.1kHz .wav @ -1dBFS.
Please contact me if you have any questions.