Wednesday, 24 September 2014

Chromatic Harmonisation

A lot of people get confused when it comes to understanding to the difference between diatonic and chromatic harmony but it's actually pretty simple. 
   Diatonic harmony is any chord that belongs to the home key - chromatic harmony is any chord that comes from elsewhere. So for instance in the key of C major an A major chord is chromatic as it contains a C# and that's a note that isn't part of C major naturally.

The trick is seeing the wood for the trees so to speak. To that end we're going to experiment with a very simple melody line in the key of G major.

B - C - D - E 

A simple harmonisation of that top line would be 

I - IV - V - IV or 

 G major - C major - D major - C  major

Into this we're going to introduce a chromatic note so our melody line is now:

B - C - D - D# - E

The D# is non diatonic (does not belong to the key of G major) so any chord we use to harmonise it will be chromatic. There are obviously a lot of possibilities but the chords that will work best are the ones that have connections with the chords before and after it. This is where the idea of false relations come in but first we need to be clear about.....

Diatonic chord movement

Take for instance the idea of a diatonic relationship of two chords a 3rd apart:

C major moving to A minor

C major is C E G 
A minor is A C E

One sounds like an extension of the other as they share two notes and the one note that changes is only moving one scale step. Obviously they're going to sound well together - they are connected by common notes. 

This can be done in the opposite direction also:

C major moving to E minor

C major is C E G 
E minor is E G B

The same logic applies. Two notes 'stick' - the E and the G. One note moves one scale step in this case the C moving to B.

False Relations

A false relation subverts this idea.

                                                          C major moving to Ab major

C major is C E G 
Ab major is Ab C Eb

Here they share one note and the two notes that move each move a semitone (chromatically) - one up and one down nicely following the rules of counterpoint. 

We hear a connection between the two chords but it's more ear catching, dramatic or 'coloured'. Have a think about the root of the word chromatic at this point and it's appropriateness in this context.

Most of the examples below use this technique. Where dominant 7ths are used this heightens the sense of tension and resolution. 

Note that the approach chord to the chromatic chord varies. The D can be harmonised with either a D or G major chord. The choices were made to maintain a 3rds relationship and to avoid stepwise movement. 

All the examples are notated and were done of the top of my head in a lesson so are by no means exhaustive. Dissect each one and look at the individual notes as they move from chord to chord. i.e voice leading. No tab here by the way! That's for losers!

To explore this concept further you could replace the D# topline note with another chromatic note elsewhere. A C# between the C & D notes would be a good choice. 

Note also that I've limited myself to major chords only. Minor, diminished and augmented chords can all be used successfully. The underlying factors that determine whether it'll sound good are the root movement and the voice leading.  

Here's video of me playing through the examples.