I've been sent a multitrack session by a singer. All audio tracks. She wants me to take it down 2 semitones for her to sing to. Obv I can leave the drum tracks alone, but I have bass, several guitar and keyboard tracks. I am new to X3 so haven't used Melodyne yet. Is that the tool for the job? or do I use Process>Transpose? Which gives the best results. Or is Melodyne more for tuning individual notes rather than taking the whole thing down 2 semitones?

Use Transpose Audio from the Process menu to take the tracks down two semitones, and use the Radius Mix algorithm. The audio will be in preview mode, which will be low quality. Bounce the clips to themselves to invoke the offline pitch transposition algorithm that gives superior fidelity compared to preview mode.

Melodyne