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Originally Posted by namiguShin
I'm interested, Tekker! Very interested...! and btw. thanks for the post above...  |
Alright, this part is basically just theoretical rambling behind the scenes of the tritone substitution (“how” and “why” it works the way it does).
Since tritone substitution is a little more difficult to see “why” it works compared to the others.
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The tritone interval has a very (VERY) strong pull towards the tonic. The tritone plays a huge part in why the V7-I progression sounds sooooo good and why if you play a diminished chord, your ear wants to hear it resolved to the tonic. So the presence of the tritone in Db7 gives this chord a similar ability to resolve to C.
The tritone can be resolved in two different ways. For example, play this on your guitar (on the G and D strings):
G--4--5--
D--3--2--
Now get that resolution out of your head (
) and play this:
G--4--3--
D--3--4--
Those are the two ways to resolve a tritone. So how do you know which one is the best to use? The trick is that intervals want to resolve in the same direction that they were altered. In other words, remember how the tritone can be called diminished 5th or augmented 4th? This is actually very important because while they are the same interval, they actually have different ways that they resolve depending on which way they were altered.
The diminished 5th was moved “inward” from a perfect 5th interval, so the notes would want to continue to move inward towards each other to resolve. This is done by moving “both” notes towards each other by one half step, which makes the diminished 5th interval resolve to a major 3rd interval. For example, B - F would result in C - E (this is the first guitar playing example)
The augmented 4th however was moved “outward” from a perfect 4th, so the notes would want to move outward away from each other to resolve. Again, move ”both” notes away from each other by one half step. For example, B – F would result in Bb – F# (the second guitar example)
Now the question is how do you know what to call it (a diminished 5th or an augmented 4th) so that you will know which way to move it? This part is a little hard to explain using only words, so let’s try some examples...
Going back to the G7 chord, in the key of C major:
G7: G
B D
F
In this case “B” comes before “F” when writing out the chord, so the order of the notes as they appear in the chord is important. Now we need to figure out what kind of an interval this is (is it a 5th or a 4th?) Let’s start on B and use the B major scale to count up to F.
B C# D# E F#
1 2. 3. 4 5
As we can see F# is the 5th scale degree in the key of B major. Therefore B - F has to be is a diminished 5th interval.
Ok, there’s one down. Let’s do the same thing for the Db7 chord used as the tritone sub.
NOTE 1: Db7 is the dominant chord in Gb major, however since we are playing this chord in the key of C major, “Cb” (as it would be called in the key of Gb major) will be called “B” because Cb is not correct notation for the key of C major. So using the correct notation for the notes is also important.
Db7: Db
F A
B
Here “F” comes before “B”, and now we can figure out this interval starting on F and using the F major scale.
F G A Bb
1 2 3 4
In this case Bb is the 4th scale degree in the key of F major. Therefore, F - B has to be an augmented 4th interval.
NOTE 2: As mentioned above, if we were in the key of Gb major, B would be called “Cb”. Since that is some kind of C note, we would find out what kind of interval it is from F to C using the F major scale. In this case, C is the 5th scale degree and therefore that would make Cb a diminished 5th interval.
So after all of that we still haven’t really gotten anywhere with our tritone subs, but we’ve set the ground work.... Now to the fun part.
The Db7 on it’s own doesn’t
really want to resolve to C. It is a dominant 7 chord with a diminished 5th interval so it wants to resolve to “its” tonic chord which is Gb. While you are satisfying the tritone in one sense by going to C, that tritone would be even more happy going to Gb. Because the rest of the chord tells the tritone that it is a diminished 5th interval and should resolve inward.
However by going to C instead of Gb, you are basically forcing it to resolve outwards instead of inwards. This of course is fine as a tritone by itself can resolve both ways, but what that tritone really wants to do within that dominant 7 chord is follow the function of the dominant 7 chord and resolve to its own tonic. Dominant 7 chords are used in modulation (changing keys) to instantly change where the tonic is even among other chords in a totally different key. So this one chord has a very powerful pull towards its tonic.
The other side of this coin is that you are playing chords associated with the key of C and your ear has already developed a sense for that tonic. So even when you throw in the tritone sub your ears still hear that tritone wanting to pull towards C instead of the new tonic Gb.
So now that you know some background for the tritone subs, you can really play around with it. For example, use the dominant 7 chord as a deceptive key change.
....What’s that? How can a dominant 7 chord be a “deceptive” key change?
Try this:
C F G Db7 C – Sounds really good and you pretty much expect it to go back to C.
Now try this:
C F G Db7 F# - Wow, never saw that one coming.
...Ok, well maybe you did see that one coming. In fact you can hear it both ways before you even play the last chord depending on which way you let your mind go. You can play around with using both methods in the same song. For example, stay in key the first time (or first few times) then throw that key change in on the same chord progression intsead of going back to original tonic.
It’s not very often that the dominant 7 chord doesn’t want to resolve to its own tonic chord, and it’s cool to play around with it.
Ok, that's it for now. Hope that helps.
-tkr