I was working on an illustration in an upcoming class for music school and thought I would share it here as well. It is a representation of a good way to think of modulations using what we call pivot chords.
A pivot chord is very simply a chord that exists in two different keys and acts as the gateway between those two keys. In other words, until you play that chord, you are playing in the old key but as you play it you transition your thinking so that you are playing in the new key.
We are modulating from Bb to C here. In this case, Dm7 is the pivot chord because it is the iii7 in the old key and the ii7 chord in the new key.
I lifted this particular example from what I did in “God of Heaven” last year. I am going to link to it in a second but before I do, I want to mention that I did one other thing in front of this modulation on purpose. I set up this mod by giving a slightly different progression three times in a row that looked like this:
Gm7 – Gm7/F – EbM7 – D7alt
After repeating it three times, an audience is expecting to hear the same thing again the fourth time. To surprise them, I changed the last chord from D7alt to Dm7 and then moved to G7 – C. I also used that entire 16 progression to build into the big verse.
The modulation starts at 2:48 in the video below. (If you don’t see a link, click here: http://youtu.be/rpV6XwGWDmM?t=2m48s )