Chromatic Mediant modulation: Can I use an omnibus progression for this?

Question

So, I am composing a piece representing winter and I am right in the middle of the piece (the piece is in Rondo form and I'm at the C section).

I started off in E major, then after being in the subdominant for a while, I went back to E major. That plagal motion is very smooth indeed. Then I switched from major to minor. Then, through a scalar motive of a minor third, I went from E minor to where I am at now, C major.

C major and E major are chromatic mediant chords. I have done smooth modulations in multiple ways, but one way in which I haven't done smooth modulations is by using an omnibus progression. An omnibus progression basically boils down to this:

Bass moves down a half step at a time

Upper voice moves up a half step at a time

Inner voices stay constant or if they need to move, the motion is minimal

Since I am writing the piece for a trio of piano, violin, and flute, it should probably be either the flute or the violin that takes the upper voice of the omnibus progression. That way the pianist doesn't run into the problem of unreachable notes(Which, as a pianist myself, I know that a ninth interval is the maximum interval size I can play and that while I can double the root and play all 4 notes in a diminished seventh, making 5 notes in an octave total, it is quite uncomfortable).

Now, I know that the second to last chord, I want to be either a B7 or a D#°7, since both of those are dominant function chords that will smoothly resolve to E major. Since I am in C major at the moment, I want to know if I can start with C major or a closely related chord to C major and use the omnibus progression to modulate to E major. I know that some keys are reachable by an omnibus progression from a certain chord and others aren't(at least if you are taking about using the dominant or leading tone chord of the new key to confirm a modulation to the new key).

But can E major be reached by an omnibus progression from C major or a chord closely related to C major? Or is the major mediant, which has a chromatic mediant relationship to C major unreachable by this method?

Answer 1

The omnibus can be used to modulate anywhere you like, as long as you allow for one or two intervening chords to help create the modulation.

The textbook omnibus basically involves contrary chromatic motion between the root and third of a dominant seventh chord; the remaining two voices stay the same. Within the omnibus progression, we have dominant seventh chords and minor triads of various roots. But there are two things about the omnibus that are especially powerful:

1. Any time we hit a new dominant seventh chord, we can use that to start a new omnibus on that chord.
2. And any of these dominant seventh chords can also be reinterpreted as German augmented sixths, which can then resolve to another dominant seventh chord to begin yet another omnibus.

So, starting on a G7 chord, the G and the B will move in contrary motion towards each other (creating a chromatic voice exchange) while the D and F stay constant.

After this initial G B D F, the omnibus takes us to A♭ B♭ D F. We can:

1. Stop and resolve this B♭7 chord to E♭.
2. Begin a new omnibus using this B♭7 chord as its basis.
3. Treat this chord as an augmented sixth (B♭ D F G♯) that resolves to D.
4. Or continue the omnibus to A A D F.

We can make any of these ultimately get us to E, but let's try option 3 (just because).

We take this reinterpreted German augmented sixth to briefly move to D (major or minor, it doesn't matter), and then we take a V7 of that key, A C♯ E G. Let's start a new omnibus here; again, the root and third create a chromatic voice exchange, so the next chord is B♭ C E G.

This is now suddenly the V7 of F, which is the Neapolitan of E! So let's take this B♭ C E G, resolve it as expected to A C F, and then from that ♭II in E we can ultimately get to our V7–I and cadence in our new key.

But as you see, this is just one of countless solutions. Going with option 2 above, we could use the B♭7 chord as the basis of a new omnibus, which immediately takes us to C♯7, which is V7/ii in E. Or, that C♯7 could start a new omnibus, the second chord of which is E7, V7/IV in E. And so on.

Answer 2

Now, I know that the second to last chord, I want to be either a B7 or a D#°7, since both of those are dominant function chords that will smoothly resolve to E major.

I agree with you that the omnibus progression has to be in B7.

But can E major be reached by an omnibus progression from C major or a chord closely related to C major?

I don't know a trick to get there from C. But I've found a chord related to C would fit fine to B7: C -> Ab.

I tried this in a 3/4 time and it sounds quite fine:

The last chord of the C section could end right in Ab (false cadence V -> bVI) or it ends on C (V7-I), followed by one measure in Ab, then the bass starts e.g. in a 3/4 (half note, quarter note ... etc.) from the 5th of Ab: Eb=D#_D,C#_C,B7__,B7__ (the B7 last 2 bars), the middle voices stay on the 5th and 7th (F#,A) and the upper part leads chromatically from B to D#

and the new section in E can begin.