3

I find that the most consonant 7th chord in all of music is the minor 7th. But why is this? Well here is how I rank the common 7th chords from most dissonant to least dissonant(theoretically there are 12 7th chords you can get from a single root but the ones with an augmented triad base are very rare):

  1. Diminished 7th
  2. Half diminished 7th
  3. Minor major 7th
  4. Major 7th
  5. Dominant 7th
  6. Minor 7th

And here are some audio examples of different 7th chords.

Here is what the diminished 7th sounds like:

http://www.easyeartraining.com/wp-content/uploads/2010/04/tevd5_ex14.mp3

Half diminished:

http://www.easyeartraining.com/wp-content/uploads/2010/04/tevd5_ex13.mp3

I often hear these 2 chords together like this:

https://clyp.it/r0tfyqi1

Half Diminished 7th goes to Diminished 7th on the same root, which then resolves to tonic.

Now, here is the Minor major 7th and its resolution:

https://clyp.it/xcjwxu4m

Major:

http://www.easyeartraining.com/wp-content/uploads/2010/04/tevd5_ex10.mp3

Dominant:

http://www.easyeartraining.com/wp-content/uploads/2010/04/tevd5_ex1.mp3

Minor:

http://www.easyeartraining.com/wp-content/uploads/2010/04/tevd5_ex5.mp3

I don't know if you would order these 7th chords in the same order in terms of dissonance but I'm pretty sure that everyone would agree that the minor 7th is the most consonant of all these 7th chords. Here is my thinking as to why it sounds so consonant. It has to do with triad overlap.

7th Chord Types and their upper and lower triads(upper triad being third, fifth, and seventh):

Diminished 7th: Diminished triad base with Diminished upper triad

Half Diminished 7th: Diminished triad base with Minor upper triad

Minor Major 7th: Minor triad base with Augmented upper triad

Major 7th: Major triad base with Minor upper triad

Dominant 7th: Major triad base with Diminished upper triad

Minor 7th: Minor triad base with Major upper triad

Now, according to this, the Major 7th and Minor 7th should be equally consonant. But I don't hear it as such. This is where chord relations come in. If you were to take a major 7th apart into its 2 constituent triads, you would have I and iii. In the key of C, that is C major and E minor. These 2 chords are closely related, but a direct modulation does not sound all that good between these keys, or at least not as good as a direct modulation to the relative minor. In contrast, with the Minor 7th you have i and III. If C is the tonic, that is C minor and Eb major. These are not only closely related keys but they are also relative keys. This makes the Minor 7th the most consonant 7th chord, at least, I think that is what makes the Minor 7th the most consonant 7th chord.

Is this triad overlap between relative keys the reason why the Minor 7th sounds much more consonant than the other 7th chords?

closed as primarily opinion-based by David Bowling, user45266, Richard, Dom Jun 9 at 17:14

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 2
    It's going to be fairly subjective, I reckon, and everyone's order will differ. IM7 chords often get confused with iii chords, as you allude. – Tim Jun 8 at 16:13
  • 2
    I don't know, why do you think that's the most consonant seventh chord? To me, at least, that's a counterintuitive result; most people I know would immediately think of the maj7 chord, probably because of its stability as the I chord (m7 is sometimes in ii-V-Is). My best guess as to why you feel this way is that the m7 doesn't have the M7 or m2 intervals, which are close enough to the octave that you perceive them as dissonant. Would you count a 7sus chord? C-F-G-B♭ can be stacked up into perfect 5ths (B♭-F-C-G); would you consider it more consonant? And as always, context is everything. – user45266 Jun 9 at 1:57
  • Me, I keep thinking that the dominant 7th chord is the most consonant of the 7th chords. It's often the basis of major-key jazz pieces, and the German Augmented 6th often sounds just like one (even if I often sing augmented 6ths with slightly off tuning). – Dekkadeci Jun 9 at 7:09
8

The minor seventh chord is indeed a pretty consonant chord, and this can be explained with objective maths. Recall that Western harmony is based on just intonation frequency-ratio. Most well-known, a major chord in JI consists of frequencies in ratio 4:5:6. Generally, a major third is 4:5 and a minor third 5:6. Now see what happens if you compose these intervals to the various 4-note chords, i.e. multiply the ratios and bring them to the lowest possible common denominator:

°7:   125 150 180 216
∅7:    25  30  36  45
m∆7:   40  48  60  75
∆7:     8  10  12  15
7:     20  25  30  36
m7:    10  12  15  18

Notice how the chords you rated as consonant, i.e. the ones to the bottom, use much lower ratios than the dissonant ones on top. The only chord of these that lies notably out of ordering by dividend magnitude is the major seventh chord, which is in the JI-ratio sense even more consonant than the minor seventh chord. I personally find it indeed more consonant than the dominant seventh chord, and similar to the minor seventh. I would propose two reasons why you perceive ∆7 as more dissonant:

  • The major seventh has in Western music a strong melodic connotation as a leading tone upwards. From that point of view, it's hard to hear that note as a self-sufficient consonant resting point. However, in Jazz it is in fact used as such, almost literally all the time (as is the minor seventh chord).
  • On most instruments, a chord will not actually come out in perfect just intonation. In particular, piano and guitar are tuned in the 12-edo system, in which the major third is approximated by 5.040/4 and the minor third by 5.946/5. Given that, the two chords will actually come out thus:
    ∆7:     8.00  10.08  11.99  15.10
    m7:    10.00  12.90  14.98  17.82
    Again, the major seventh chord looks actually more consonant on paper, however the top note deviates further to the top, which makes it perhaps stand out a bit sorely to your ears, whereas the too-low minor seventh may become rather subdued and inoccuous.
  • I'm glad that this is a proposed explanation rather than "this is the way it is, blah blah blah Just intonation and prime numbers". Consonance and dissonance are extremely touchy subjects, and there could be a million reasons why OP even ranks the chords this way. +1 – user45266 Jun 9 at 2:02
  • Two questions about the JI chart: if dom7 and maj7 both start with a major third why is the first number for dom7 20, but maj7 8; how to read the result add all the numbers so dom7 is 20+25+30+36=111, and maj7 is 8+10+12+15=45, so maj7 is less dissonant that dom7? – Michael Curtis Jun 10 at 14:48
  • @MichaelCurtis addition of those numbers doesn't seem particularly meaningful, I'd rather consider the geometric mean or something like that. But for the sake of comparison it doesn't really matter: ∆7 is more consonant. — The reason it's 8:‥‥ in the ∆7 but 20:‥‥ in dominant-7 chord is that the two major thirds in the ∆7 share part of the same “starting ratio”, i.e. 5:4 and 3:2*(5:4). You only need to augment by a factor 2 (from the perfect fifth between the starting points). In the dom-7 however, you stack a minor third 5:6 on to of the fifth, and that doesn't share the 4 starting point. – leftaroundabout Jun 10 at 18:34
  • @leftaroundabout, I'm not really proposing what to do with the numbers. I simply meant I don't know how to understand what they mean! I only understand the numbers are some kind of objective measure of consonance. Can you explain a tittle how to understand the results? – Michael Curtis Jun 10 at 18:42
  • One way to understand the numbers is, a chord can be considered as a subset of overtones of a shared sub-fundamental. So, a C∆7 chord consisting of C4 E4 G4 B4 has a “virtual fundamental” C1 (factor 8 = three octaves); the combined waveform is periodic at that frequency. The waveform is consistent. OTOH, for the more dissonant chords that fundamental is much deeper, generally in the infrasonic, and the waveform doesn't really repeat at all (when it eventually would repeat the phases have already drifted apart and the ear can't latch onto it anymore). – leftaroundabout Jun 10 at 18:58
1

The main difference between these two chords is the interval between the 7th and the (octave of) the root. For a major 7th chord, it is only a semitone, which lends bite to the sound. For a minor 7th chord, it is a whole tone. This together with the presence of two perfect 5ths makes the chord very stable.

Not the answer you're looking for? Browse other questions tagged or ask your own question.