Dissonance

Tension is intended

The page Harmony describes, already with two notes sounding at once, how combinations of notes sounding together differ: some seem calm and coherent, that is consonant. Others seem full of friction and demand continuation, that is dissonant. Neither is “better”. Music lives on the alternation: dissonance creates tension, consonance releases it.

The reason lies in physics. On the page Interval Ear Training it says: behind every interval lies a frequency ratio. The octave is 2:1, the perfect fifth 3:2, the perfect fourth 4:3, the major third in just intonation 5:4. The simpler the ratio, the calmer and more fused the combination sounds. Once you have understood this, you no longer hear consonance and dissonance merely as a matter of taste but also as an acoustic property.

Dissonant intervals

The page Intervals describes each interval with its ratio and character of sound. The dissonant ones are:

In between there are gradations. According to this page the major second is distinctly more tense than the third or fifth, but by far not as full of friction as the minor second. Melodically the minor second, according to the page, often sounds painful, plaintive or threatening. In equal temperament the tritone has no simple ratio, which, according to the exercise page, makes it floating and undecided.

Dissonance resolves

The dominant seventh chord G7 consists of G–B–D–F. The article The leading tone describes what happens in it: the B wants to go a semitone up to C, the F a semitone down to E. Between B and F lies a tritone, the most unstable interval of the system. If you resolve both notes at once, you land on C and E, two of the three notes of the C major triad. Hear for yourself how the tension is released:

The cadence G7 – C is, according to the article, so inescapable that it forms the ending of very many pieces of Western music between 1650 and 1900. If a piece stops on the dominant, the ear goes on waiting for a resolution that does not come.

What counts as dissonance changes

The boundary between consonance and dissonance is not fixed. The Intervals page names three examples:

• The major third: In the Middle Ages it counted as impure and was avoided. Only from the Renaissance was it accepted as a full consonance. The article Why the fifth sounds hollow adds: in the organum of the 9th to 12th centuries thirds counted as dissonance.
• The fourth: In classical counterpoint the fourth between bass and upper voice counts as a dissonance that has to be resolved, although between other voices it sounds perfectly consonant.
• The major seventh: In traditional harmony it was avoided for centuries as an unresolved dissonance. Only jazz made it a characteristic pleasing sound, for instance in the maj7 chord as the trademark of bossa nova, smooth jazz and romantic ballads. There the tension is no longer resolved but used as a colour.

Dissonance in the score

An example of friction in a single melody is provided by the beginning of Beethoven's piano piece:

Piano

• Für Elise Ludwig van Beethoven, WoO 59 · piano · 3 pages

  The piece begins in the upbeat with E–D♯, a semitone step, so a minor second. In bar 1 the melody continues to sway: E–D♯–E–B–D–C. The step E–D♯ is the opening that the Intervals page gives as an example of the minor second.

Common mistakes

• Equating dissonance with “wrong”: The page Harmony says explicitly that neither is better.
• Always wanting to resolve dissonance: In jazz the major seventh also appears without resolution, as a colour.
• Always taking the fourth for consonant: In classical counterpoint it counts as dissonant above the bass.