modulating by a tritone

Question

I have heard that modulating by diminished fifth/tritone is the hardest of all modulations. Interestingly my non-musician husband has just composed a tune with a smooth tritone modulation (ie. from C to F sharp below). Apparently the key to his success was: the last chord of his tune before modulation happened to be G major, which continued to F# major (tonic of the new key). In other words, root movement by a semitone/minor second.

Does anyone have other strategies for a successful tritone modulation, especially if the tune does not lead to such a "semitone/minor second" chord progression?

Answer 1

One way to see and realize a modulation by a tritone is in two steps of a minor third. A modulation by a minor third corresponds to a change from major to minor (or vice versa). From F major to B major this could look like this (these are keys, not chords):

F major => F minor / Ab major => Ab/G# minor / B major)

One example of a realization of that idea is the following progression:

|| F | Bb Bbm | Db (C#) | C#m F#7 | B ||

Another important thing to notice is that due to the tritone interval between the roots of the two keys, also the V7 chords of both keys are a tritone apart. This means that the V7 of the first key is the tritone substitution of the V7 of the new key. Example: C7 is the V7 of F major, and F#7 is the V7 of B major. Note that C7 and F#7 share (enharmonically) the two most important chord tones: the E (3rd of C7, 7th of F#7) and the Bb (A#) (7th of C7 and 3rd of F#7). This is why these chords can replace each other, which can of course be used for modulating between the two keys. The tritone interval of both V7 chords (E - Bb/A#) can resolve in two ways:

E -> F Bb -> A (corresponding to C7 -> F)

or

E -> D# A# -> B (corresponding to F#7 -> B)

Answer 2

A very traditional way would be to pivot from a Neapolitan sixth chord (bII⁶) in your first key to V⁶ in your second key. For instance, in C major, you'd have a first inversion Db major (this is your Neapolitan) which becomes the dominant of Gb, and resolves to Gb, modulating a tritone.

If this is too abrupt for you, you may want to smooth out this modulation with a brief transition to the parallel minor (C minor in this case) and arrive at your Db chord through chromatic alteration of of a iv or ii°. For instance, CMaj - Fmin - DbMaj - GbMaj.

Answer 3

There are many different ways to approach this, but I think the simplest way would be to take advantage of chromatic movement similar to the one in your examples.

There are two simple ways that I can think of to modulate that way off the top of my head. That use chromatic movement and dominants to pull you to the new key.

The first one is rather simple. Using your example of going from the key of B major to the key of F major you would start on the tonic chord B (I of B major) then go to C7 (V7 of F major) chromatically then go to F (I of F major). It's very simple and gets the job done.

The second one is a little more complex, but personally I think sound better. Using your example of going from the key of F major to the key of B major you would start on the tonic chord F (I of F major) then go to BbMaj7 (A#Maj) (IV7 of F major) then go to Bb^ø7 (A#^ø7) (vii^o7 of B major) chromatically then finally go to B (I of B major).

Both of these need to be voiced correctly to sound right, but should get the job done. If you are interested in modulating to distant key I recommend studying impressionist pieces as they tend to modulate to distant keys pretty often in creative ways.

Answer 4

Another way to modulate by a tritone is by using the French augmented sixth chord of the original key which contains the same notes as the... French augmented sixth chord of the destination key.

For example, the French augmented sixth chord in the key of C is D F# Ab C, and, in the key of F#, G# B# D F#.

If you write the French sixth of C in root position, you'd have the French sixth of F# in second inversion, and afterwards you can resolve smoothly to the V or the I 6/4 of F#.

Answer 5

I actually just composed a piece that modulated a tritone up! My methods were... unconventional, but hey, it worked!

So basically, I had this basic chord progression: | Em | B | C | Adim Fdim |

And I wanted to modulate up to Bb minor. So, what I did, was resolved to E diminished instead of Em. Then, I had the lead voice play a Bb over it. Then, after a measure, I played the Bb minor and had the lead voice continue playing Bb so that the transition was smoother.

When you do this, you do need to establish the chord progression again because if you don't, it feels offset (because it was).

Basically, my point here is, a lot of things are possible. And, the only way to find out what is possible is by expirementing.

TL;DR I used the diminished 1 chord to modulate up a tritone