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I have seen a lot of people say that the minor second is more dissonant than the tritone. I however don't think of it that way. Don't get me wrong, the minor second is quite dissonant but to put it simply, I think the tritone is the most dissonant interval, not just a very dissonant interval. Part of the reason is that it divides the octave cleanly in half. Now you might think that octave symmetry should make it very consonant. But in fact, this usually turns out not to be the case.

For example, the whole tone scale, as a scale is relatively consonant. But harmonically, it is extremely dissonant. All the fifths are either diminished or augmented. This makes for some weird harmonic progressions. So actually, symmetry is kind of a guarantee for extreme dissonance. That is, unless you consider Dorian to be symmetric(which most don't, when most people say symmetry in music theory, they mean octave symmetry, not palindrome symmetry).

Another reason I view the tritone as being more dissonant has to do with the way it resolves. In a minor second, only 1 note wants to resolve, thus making the minor second want to resolve to a unison. In a tritone, both notes want to resolve into either a third or a sixth via contrary motion. When you build chords based on the tritone, this dissonance is further emphasized. At its most dissonant without extensions, you get 2 tritones with an overlap distance of a minor third or to put it more simply, a diminished seventh chord. This is easily the most dissonant seventh chord that exists and the most urgent to resolve.

Sure, you can delay the resolution of a diminished seventh to build up tension in the piece. A great example of this is the First Movement of Beethoven's Fifth Symphony, where Beethoven repeats the same diminished seventh for more than 2 measures more than once such as here(he does a lot of melodic repeats of the diminished seventh i.e. writes the diminished seventh using the melodic and rhythmic contour of the Fate Motif, but these, even at fortissimo aren't as powerful as the harmonic repeats he does of that same chord i.e using the diminished seventh as a rearticulated suspension):

But the diminished seventh has to resolve, be it to a consonant triad or to a dominant seventh chord. The reason it has to resolve? Those 2 tritones that make up the diminished seventh chord themselves have to resolve. Combining this with its typical harmonic usage as either an extension of dominant function(when it shows up in a major key, it usually is extending an already present dominant function) or as is often used in minor keys, as a substitute for the dominant seventh, leading to a cadence that is pretty much exclusively used in minor, that being vii°7 - i, and it just has to resolve to either the tonic or a dominant seventh. Another common harmonic usage of this chord is to help modulate to distantly related keys, usually minor keys. This again involves resolving the chord to either the new tonic or to a dominant seventh which then resolves to the new tonic.

So, given that the tritone alone has 2 notes that both want to resolve in contrary motion and that the diminished seventh, which is the most dissonant of seventh chords has 2 tritones, is the tritone the most dissonant interval?

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    "most" by what measure? Some will try to answer by comparing interval ratios, other by some aesthetic quality of intervals. – Michael Curtis Dec 10 '19 at 20:21
  • Do I really have to specify the measure by which the dissonance comparison is made? I mean, I have already mentioned in the question 3 things that make the tritone a very dissonant interval, its octave symmetry, the way the interval resolves(which is where I compare it to the minor second, another dissonant interval), and how that dissonance of the tritone gets emphasized in seventh chords with a tritone in them, especially in diminished seventh chords that are made out of 2 overlapping tritones. – Caters Dec 10 '19 at 20:37
  • That question that you linked to only goes into the interval ratios. I don't always trust the interval ratios when it comes to the consonance or dissonance of an interval or a chord. Nor do I always trust the interval's position in the harmonic series either(that would make the tritone more consonant than the perfect fourth, which just isn't right). That is why I mentioned 3 things besides the ratio and the harmonics that are related to the tritone's dissonance, the octave symmetry, the way it resolves, and how the dissonance gets emphasized in seventh chords, especially diminished sevenths. – Caters Dec 10 '19 at 21:52
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    @Caters, "Do I really have to specify the measure by which the dissonance comparison is made?" Yes. The word "most" necessitates a ranking. How can you do that without a measure or getting bogged down in the aesthetics of harmonic context? Just change the context to the blues and the notion of dissonant tritones completely changes. – Michael Curtis Dec 10 '19 at 22:34
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Actually, this is totally about the music you've been listening to when you grew up. If you've grown up listening to songs that are dominated by Major or Minor scales, You'd find other intervals dissonant. Say you grew up in Arab, They have a 24 tone tuning and Tritone or Minor 2nd will hardly sound dissonant for you.

It's very relative. If you listen to the messiest Chord Progression for more than thrice you'll get used to it. You listen to a bad mix down again and again, you'd probably get into an illusion of thinking that its good which is why producers and DJs don't normally spend too long mixing the same song. If you've been listening to all Heavy Metal stuff, Tritone will probably sound very consonant to you. Listening to a lot of Classical Music might get you used to a lot intervals too.

If you want to know only about these two intervals in your question then We can take a more Physics-y take on it.

Waves of a minor 2nd and Base tone, enter image description here sin x takes approx. 17 periods to concord (not really as our modern tuning is irrational) with a minor 2nd

Waves of Tritone and Base tone, enter image description here These concord much earlier at approx. 5 periods

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    Huh, the heavy metal I listen to tends to be power chord-heavy (though often with weird chord progressions). – Dekkadeci Dec 11 '19 at 17:27
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Some will say this question is opinion based and the answers are subjective.

If you play 100 times diminished 5ths you’ll find that the tritonus sounds consonant.

The same you will find if you play often enough major 7ths and minor seconds:

Mikrokosmos 144

you’ll get used of it and the sound wonderful!

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    This is opinion, not fact – Carl Witthoft Dec 11 '19 at 15:17
  • It is a fact that if you listen long enough to intervals that are called dissonant that they are sounding consonant. What about the thirds which were called dissonant relativ to perfect fifths and octaves? Richard wrote in his answer to the related question: 9 It can be tough to define exactly what "dissonance" is (it changes throughout history, and it changes between genres), but Paul Hindemith created his own theory regarding ranked dissonances. .... And today now it's me who ist creating his own theory :) – Albrecht Hügli Dec 11 '19 at 16:38

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