Before you replace chords with 3 or 4 notes with those with 5 or 6 notes (or even more), re-harmonize a melody by applying these 2 complementary strategies recursively (i.e. each is applicable to the result of applying them, so you can do it in many passes) to chord changes:
- 1) replace one chord with two (duration of 2 chords in new version =
duration of 1 original chord, OR duration of 3 chords in new version
= durations of 2 chords in original)
- 2) replace two chords with one (sticking to one of them and make it
last longer)
While you do so, make sure every step of the way, your chord substitution works with the melody: there is no one-size-fit-all replacement for something like 1-5-6-4 because it all depends on the melody. Why would you want to do 2) if you want your 'pop' chord changes to sound more 'jazzy'? That is because simplifying changes allows you to complexify them later IN ANOTHER WAY (e.g. add passing chords, etc.) to your taste.
Tactics for 1) are:
- 1a) Add a chord that shares 2 notes with the the current chord,
somewhere in time between the current one and the next one. (where in
time? you choose!) e.g. Add a minor triad with the same root if the
current chord is a major triad (or add a major for a minor). e.g. Add
a chord whose root is a third above or below (remembering to share 2
notes and checking if it works with the melody). For something like a
G7 (in key of C), this can mean not only Bm7(b5) or Bdim7, but also
BbMaj7 or Bb7 (and more... use the melody as constraint and
inspiration).
- 1b) Add a chord BEFORE the current one (usually between this chord
and the previos chord, but you can do this even to the first chord:
it just means you need to start the song sooner) whose root is a 4th
below (or 5th above) the current one. Adding a so-called dominant 7th
type chord (i.e. a chord with major 3rd and minor 7th above the root)
before seems to work well in most cases, but keep other choices in
mind too. If the current chord is already a dominant 7th type chord,
adding a minor triad (or m6, m7, etc.) before or a m7(b5) there seems
to work well also (other choices are still there for you).
Directions for 2) are:
- 2a) Try to get rid of "passing chords". Passing chords in harmony are
like passing notes in melody: they are usually in rhythmically weaker
positions 'linking up' pitches more important structurally 'in the
flow' (usually in rhythmically stronger positions), and they can be
though of as 'diatonic' if they are within the scale in use now (or
nearby), or as 'chromatic' if they are not; unlike classifying
passing notes in melody, which is a pretty 'either-or' matter,
passing chords can be thought of as having shades or degrees of
chromaticism (i.e. the more notes 'outside the scale' a chord has,
the more 'chromatic' it is said to be). Remember: you can get rid of
not only chromatic passing chords, but also diatonic ones, and the
chords will still (somewhat) work with the given melody.
- 2b) After removing 'obvious' passing chords, less 'obvious' ones will
seem to surface. Now, try to figure out what tactics the original
maker of the chord sequence has used to complexify it. Was it 1a)
here? or 1b)? or 1a-then-1b or 1b-then-1a? Usually for pop, as you
undo this level of complexity, each section (or sections or even the
entire song) can be boiled down to a very simple cadential
formula (e.g. called 'authentic' or 'imperfect' or 'deceptive' or
'plagal' etc. by older theorists, 'some sort of II-V-I' by jazz
theorists). As you strip away more and more chords from the original,
it will sound less and less like it, WHICH IS WHAT YOU WANT.
Using these strategies involves trial-and-error (so the more you do it, the more proficient you would be at getting to a solution you like), and doing it with your instrument, score AND PENCIL helps.
After you have re-harmonized a 'pop' melody using the mentioned strategies, you are ready to 'jazz it up'. By having done the re-harmonization that way, you would have already noticed what scales are implied by the chord changes and the melody from moment to moment in the song. Use those scales to construct chords with more notes to replace the simpler version by starting with the given root and stacking 3rd's up.
For example, if the scale is C minor and the current chord's root is F, the chord (spelled from bottom up) can be F A (or Ab) C Eb G B(or Bb) D. Then look up the symbol for your the chord you want (from a guitar chord chart book or software or webpage etc.) and/or start considering the voicing of the chord (esp. if you are doing it on keyboard or something like it - like xylophone).
But what if you have chosen chromatic (passing) chords in your solution? In that case, figure out what scale is implied by your current (and chromatic) chord, and use that instead to construct your 'more-jazzy' chord just for the moment.
The reason why some chord changes sound more 'jazzy' is because they manage to make the listeners think of a key (which implies a scale) in mind by structuring phrases or sections that boil down to a simple cadential formula, but 'on the surface' ('above' that 'boiled-down' level) from measure to measure (or even from beat to beat) they use as many chromatic (i.e. outside of the scale) pitches as possible. It is a tricky balancing act because if you CONSTANTLY use only pitches outside the key, eventually the listeners' mind would flip to deem those pitches as defining a new key. So, to created that jazzy impression, don't just go for those 'outside the key' pitches; instead, keep enough 'inside the key' pitches to trick the listeners into thinking of a key, while staying one step ahead by surprising them with pitches 'outside' of their expectations IN-BETWEEN.
For a 'pop' audience, some tactics to do so are:
- i) To construct your dominant chords, instead of using only major and
minor scales, use diminished scale e.g. G Ab A# B C# D E F to
construct G13(b5#5b9#9) for the key of C, or diminished-wholetone
scale (e.g. the one starting on G has the same pitches as Ab melodic
minor) to construct G13(b9#9#11) for the key of C. For chord
constructions of non-dominant chords (e.g. tonic, etc.), using
melodic minor or harmonic minor scales allow for more opportunities
for 'more jazzy sounding' m7(b5) [i.e. an 'inversion' of 'minor triad
add major 6th' chord] or mM7 [minor 3rd and major 7th above root]
chords (and similar chords with more notes). 'Pop' songs seem to use
quite a bit of dim7 chords (and similar chords like 7(b9)) too, so it
is up to you to decide if using them makes your song more 'jazzy'.
- ii) Apply 'tritone substitution' to your dominant chords (which can
be thought of a frequently-used and formulaic application of strategy
1)-then-2) or 2)-then-1) ... but that is really stretching it ... ).
e.g. replace G7 in the key of C with Db7. Not enough dominant chords
there to do this? Backtrack from you current attempt to 'jazz up
chords by added more notes to them' and go back to applying
strategies 1)&2) more in order to put more dominant chords there in
the first place! (for this purpose, let's just say any chord with
a major 3rd and minor 7th AND going into a next chord whose root is a
4th above or a 5th below is a dominant chord). This is quite doable
for many 'pop' songs. If the melody allows it, you may even be able
to simplify-then-complexify your chord changes to a point for
'Coltrane substitution' to be applicable (for 'pop' melodies,
this is less often doable than 'tritone substitution', but far from
impossible). Needless to say: Coltrane sounds REALLY jazzy!!!
