Let's say you are writing a piece (or a section of a piece) in a particular mode, or you are using a particular scale. You just wrote the best motif ever and now you are experimenting with what chord should follow and want to transpose the motif so that the relationship of the pitches stay the same to the new chord but still within the root scale of the piece/section.
Scale Assistant is a function in Cubase which lets us quantise our musical content to a specific scale, and it basically takes the notes we write which are out of the target scale and moves them to the closest note within that scale.
How do we setup this feature?
1 - First of all, we need a midi event
2 - Now, open the Key Editor (you can do that double clicking on the event, typing OPT + CMD + E, or going MIDI > Open Key Editor). Make sure the editor is selected so that the inspector is showing the editor's options (a white frame around the window will show you which part of the project is selected)
3 - On the Left Inspector Panel, open the drop down menu Scale Assistant
4 - Set your target scale
5 - Tick Show Scale Note Guides if you want the background of the piano roll to show you the notes which are within the target scale (white keys)
6 - Tick Snap Pitch Editing to snap pitches to the Scale Assistant settings while editing
7 - Optional: if you want Cubase to snap your notes to the target scale live while playing/recording, tick also Snap Live Input
8 - All set! We can now duplicate our midi event and move it around the scale with the up/down arrows while keeping it within the target scale's notes
9 - Note that this function will remain active for any other midi events in your project, so make sure you deactivate it un-ticking again Snap Pitch Editing (and the other options currently active), to avoid unpleasant surprises.
Here is a short video to briefly show you the process and demonstrate how the notes will snap to the target scale once the function is activated:
This is a really useful feature, for example, when working on new material and experimenting with a motif and chord progressions: with a few clicks you can hear how your motif would sound on a different degree of the tonic center, different key, if you need to modulate and try out different keys, or just to creatively experiment with new things and find unexpected results.