Diminished Seventh Chords

1. Diminished Seventh

A little while back, I introduced a chord “Minor Flat-Fifth“. Its 5^th is lower than usual, which is called a “diminished 5th” or “tritone”, producing an unstable and eerie sound.

Here, by adding the note la along the major scale, it becomes the “Minor Seventh Flat-Fifth” chord. But what if you add la♭ instead of la?

The chord is termed a Diminished Seventh chord, symboled as “dim7“.

When examining the relationship between chord tones, re and la♭ is also a tritone interval. This chord has the “two pair” of strong dissonant tritones, holding an intense impact.

If this were poker, the victory would be certain! This double tritone creates a highly potent dissonance, generating an effect that renders the musical scene remarkably unstable. In this session, we will discuss the characteristics and basic usage of this chord.

2. Characteristics of dim7

Dim7 has unique characteristics besides “tritone two pair”.

Equidistance

Firstly, the Diminished Seventh has all its chord tones arranged at equal distances.

They are separated by 3 semitones each. Even the top ‘F’ and the root ‘G♯’ are 3 semitones apart when excluding the octave difference. In essence, it means that a dim7 chord is made by dividing into four parts the spiral of an octave, which completes one cycle in 12 semitones.

By looping these semitone steps, a beautiful cross is drawn.

Symmetry

The equidistantness causes an even more interesting phenomenon. For instance, if you try to create a Diminished Seventh chord with G♯ as the root instead of B, it ultimately summons the same group of chord tones.

The lineup remains the same, differing only in who becomes the root. This occurrence is due to equally dividing the 12-note loop. Therefore, G^♯dim7, Bdim7, Ddim7, and Fdim7 all have the same chord tones¹.

Hence, the Diminished Seventh chord is best understood as “forming one family with four members”.

Three Families

With 12 notes on the keyboard, it should be possible to create 3 families each with 4 notes. Specifically, it looks as follows.

C-E^♭-G^♭-A Family

C^♯-E-G-B^♭ Family

D-F-G^♯-B Family

This fact, “different chords, but having the same chord tones”, can be utilized for modulation techniques as well. It’s truly an intriguing chord feature.

3. Uses of Diminished Seventh

dim7 is a chord with a strong characteristic. The approach to mastering its usage relies on memorizing patterns that define when and how to use it.

Horror-oriented Use

One good usage is to create a horror soundscape deviating from the ordinary major/minor tonality, fully utilizing its murky and creepy sonority coming from the “two pair” of tritones.

G_dim7B_dim7A_dim7B_dim7

Just by connecting dim7 chords in such manners, a perfectly fitting horror background music is created. This can be quite valuable in game music or movie soundtrack.

This depiction integrates the dim7 zone into the middle of a classical minor key world. Dim7 chords wield a top-level dissonance, so haveing them as options is an important skill for musical expression.

Pops-oriented Usage

For the subsequent chord after a dim7, the most standard approach is to place a half-step higher major/minor chord, smoothly resolving the dissonance and proceeding to the next section with clarity. Especially in pop music, it’s common to place V_dim7 right before VI_m.

IV_Δ7V₇V_dim7VI_m7

It plays a role close to the secondary dominant III₇. There are several patterns for using dim7 in pop music, and this will be introduced again in Chapter IV.

Auxiliary Diminished Seventh

In jazzy styles, it’s standard to use V_dim7 instead of V₇.

VI_m7II_m7V_dim7I_Δ7

Under the context, the dissonant dim7 sound works as somewhat sophisticated complexity.

Similarly, turning I_Δ7 into I_dim7→I_Δ7 creates a small tension/release scenario like sus4.

II_m7V₇I_dim7I_Δ7

The orthodox ii-V promises to resolve to I, but it intriguingly postpones resolution with a peculiar chord, the dim7. It’s fascinating in its unusualness; while it might be challenging to carry a melody on it, it easily fits into instrumental tracks.

These dim7 applications are referred to as Auxiliary Diminished Seventh².

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Chapter III has introduced various “spicy” chords, but in terms of its eccentricity, the diminished Seventh chord reigns as the king.

Structure Composition

Upon examining the intervalic structure of the chords once more, minor seventh, minor seventh flat-fifth, and diminished seventh are only different from each other by a half step.

In this manner, it might be helpful to memorize them in relation to the minor seventh: by lowering the 5^th and then the 7^th.

Ti–la is a “minor 7th” interval, whereas ti–la♭ is even shorter, and called a “diminished 7th“, which was introduced at the beginning of Chapter III. Something shorter than “minor” leads to the term “diminished.”

Root, minor 3rd, diminished 5th and diminished 7th make up a diminished seventh chord… Now you’ve reached the stage of mastering some quite difficult chords! Well done.

Summary

• The chord formed by further lowering the 7^th of m7(♭5) is referred to as the “Diminished Seventh” chord.
• Diminished seventh chords produce an extremely unstable sound and is utilized in many ways.
• Changing I and V to dim7 (or inserting before them) is called “Auxiliary Diminished Seventh.”

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