Hello!!
In simple terms you need to hide it in another signal at a different frequency or amplitude (FM or AM) so that they're not having the same angle or amplitude. But, if they seem to share some of the parts, then they might get aliased which might pose difficulty in recovering the signal. But, if you have the flexibility to choose the hiding signal (voice) then, it becomes a simpler task to achieve.
Rest, such as deliverables, timeline etc. I can discuss with you when you're online and ready for a chat. After the discussion, we can finalise the bid amount and time. Thanks!!