Originally Posted by: LeedoggWhat about non-relative key changes?

It's possible to go to any key. There is always a common chord. Even when there seem to be none, there's the diminished 7th chord. Which in this chord, each note can be considered the root. Also chords can be altered, to in turn create a common chord.

Is that something that only jazz dudes do?

No. All styles of music have modulations. Beethoven was known for his bold and dramatic key changes. Bach wrote the "well temper clavier" to demonstrate to uses of modulation.

What does that sound like?

Chords themselves can pretty much go anywhere. What matters is the voice leading of the chords. Dissonance is a good thing. Take the tri tone substitution with a common chord progression (ii-V7-I). Instead play this ii - bII7 - I. This is a perfect case where dissonance is better.

The most common problem that newbies occurs when dealing with modulation is the use of the tonic dominant function. Anytime a modulation occurs it's good to play a cadence at the point of modulation. This secures the key change.