Hi
Does anyone know if Cubase has a function to detect the key of a midi bassline, the reason being I have lots of midi basslines that I want to use, but need to know what key they are in.
It doesn’t matter what key they’re in, if you use chord track Cubase will convert them to any key/chord progression you want anyway. Just set the track to follow chord track and use single voicing/bass mode.
You can also import them into apache midi insert arp or chord pads as arp patterns which will play back in key.
(I think) That mode will only play the root note of the chords (i.e. in this case ‘C’) you want to pick single voicing, and then Bass in the second box, rough guide here:-
Although that guide says that root note mode is suitable for bass… I guess use what works for you (or the MIDI loop you’re bringing in). It’s a very powerful element of Cubase if you learn the different modes. 
In the chord track you can set chords and their root/bass note for each chord symbol - so that’s important if you want the bass to walk (i.e. Am, Am/G, Am/F# etc.) It will all dynamically change as you change the chords in chord track, very cool.