Often you will encounter the set of roman numerals I to VII in music literature. What are these? Very simple, they are nothing but names for the the seven notes in a scale (assuming you use a scale with seven notes – 5 note scales use only I..V). They are called scale degrees.
For instance, look again at the notes in the C major scale: they are C, D, E, F, G, A and B respectively.
Now let’s display them as roman numerals You can do this by selecting the appropriate value in the labels combobox:
The result looks like this:
This the same scale, the same key, but just different labels. Why bother then? Well, this allows you to indicate the n-th note of a scale regardless which type of scale/key you are using.
For instance compare with D Major:
Original notation: D, E, F#, G, A, B, C#
And its roman numeral notation:
Did you notice how the I .. VII set has shifted two positions to the right? That’s because we now start at D instead of C.
Why is scale/key-independent note labeling useful? One example is when you want to specify the root notes of a series of successive chords to play (called a chord progression) within a scale/key, without knowing up-front what that scale/key is. That way it suffices to write down the chord progression just once as roman numerals (e.g. I–III–IV) which you can then apply to a myriad of scale/key combinations later.
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