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BIAB can create different harmonies based on the melody. Why not generate some in BIAB based on your melody line and chord progression, and then sing those generated notes as your harmony.

I agree 110% with that statement.

To sort of answer your question, follow your melody and the notes in the current chord it is using will you give you your 3rd and 5ths etc. for the vocal harms.

Biab will allow you to generate a 1up / 1 dn with the TC Helicon in it. If you are going to use the TC Helicon, make sure your lead vocal track is mono format, clean (no reverb/chorus) and in tune PRIOR to generating the TC Harms with. You can send them (harms) to their own, mono tracks and then sing/record them and they will sound natural vs the robotic effect the TC comes up with.

Mixing them with the PG pre-set vocal effects will allow them to sit in the mix and sound fantastic, if done properly.

Trax