About traditional keys, tonal center and key changes

Key is a fundamental concept of tonal music, which developed during a certain era and still predominates in Western music to this day.

Figure 1. Chords strictly built from the steps of the horizontal C Major scale

Many musicians think of key as being a scale, but keys do not have such a strict boundary. Key is a rather broad term for the harmony a piece of music is moving in. Modern music uses a lot of secondary dominants and other loosely related chords that are built from notes well outside the scale that lends a key its name. Still, a listener recognizes the key by characteristic chord changes (cadences) and melodies.

Key Changes (Modulation)

A change of key is also known as Modulation. Synfire is comparatively skilled in the recognition of keys. However, due to the ambiguity mentioned above, it is a matter of judgment where exactly a key change is taking place. Concerning key changes, the decision is always with you, the composer.

There are widely differing notions of modulation and whether it requires preparation and affirmation. You should not get distracted by such debates. In modern music, you may jump from one key to another in an instant, provided it makes sense to an unsuspecting listener. And that is a matter of experimentation and testing.

With some jazz styles key changes are so frequent, a "key" printed on a score is merely a means to keep it all meaningful and readable.

Note: Every Harmonic Context in a progression has a key assigned. If the key of a context is different from the previous, you have a key change. It's as simple as that.
Tip: As a general rule of thumb, if you change key, don't do so in the middle of something, but rather between clearly cut sections. Also you shouldn't change too many things at once, so there is something a listener can hold onto while your continents are drifting. You get the idea.
Tip: After your progression moved from one key to another, you should emphasize a few chords that are unique in the target key.

Tonal Center

The Tonal Center is what you assume is the root of the Major/Minor key you currently work in, regardless of the Scale Set you might use to browse interesting chords. It determines the coloring and spelling of chords and scales and somewhat influences the scale selection preference for progressions.

The tonal center lends a functional meaning to all chords. The term was coined in classical music theory, but can be a useful tool for exploring key changes in any musical genre.