You can input any chords you want on the chord track. You can put any notes you want in any scale, regardless of what’s on the chord track. If you tell the track to follow the chord track, it will move (fix, improve, make more musical) your midi data to match the chords on the chord track. So, the Cubase chord track is like a pre-midi filter that can change your midi data in real time, and the chord assistant tries to help you make better choices about what sounds good.
The common 1 - 4 - 5 - 1 pattern you hear in most pop music is, for example in the key of C Major,
C major, F major, G major, C major. Why? Because if you number the notes in the scale:
8 C (octave)
The 4th note, F, is a fourth (that’s why it’s called that) - four notes up from C
The 5th note, G, is a fifth (that’s why it’s called a fifth) - five notes up from C
The key is the root note the scale starts on, that’s your 1 chord. The scale is created by the notes that follow the key, from 1 to 7 (whole whole half whole whole whole half, for a major scale).
The chord assistant helps you find chords that commonly come between two other chords, logically, or based on standard music theory. If you ever tried to write a bridge, you need to go to some other chord, different from 1, 4, 5, 1 (or whatever pattern your song happens to use) and get back to the root chord again. Chord assistant helps you write bridges and transitions based in common practiced music theory. If you drag the slider bar past 1 toward 8, you’ll see more unique, original, complex chords suggested. That is, you’ll get more types of interesting chords, than just 1-4-5-1. Farther to the right are more jazzy chord structures with 7ths, 9ths and diminshed tones.
If you drag a note on a part following chord track, the note background turns green if the note is in the chord, blue if its in the scale, and red if it’s neither. Red notes sound dissonant (that is, bad-sounding, based on the key/chord). So, for example, playing an E flat with a C Major chord - the E flat will be a red note, because it’s neither in the chord nor the scale.
You can generate harmonies from a vocal track following the chord track, and choose if they’re 2nd supporano, alto, tenor, etc. You can also generate chord track changes from an existing part.
I saw Greg Ondo demo all of this at a Cubase 7 meetup and a lot of jaws hit the floor.
Hope that helps!