Dissonance
music, dissonance is the quality of sounds which seem "unstable", and have an aural "need" to "resolve" to a "stable" consonance. Both consonance and dissonance are words applied to harmony, chords, and intervals and by extension to melody, tonality, and even rhythm and meter. Although there are important physical and neurological facts important to the understanding the idea of dissonance, the precise definition of dissonance is culturally conditioned—definitions of and conventions of usage related to dissonance vary greatly among different musical styles, traditions, and cultures. Nevertheless, the basic ideas of dissonance, consonance, and resolution exist in some form in all musical traditions that have a concept of melody, harmony, or tonality.
Additional confusion about the idea of dissonance is created by the fact that musicians and writers sometimes use the word dissonance and related terms in a precise and carefully defined way, more often in an informal way, and very often in a metaphorical sense ("rhythmic dissonance"). For many musicians and composers, the essential ideas of dissonance and resolution are vitally important ones that deeply inform their musical thinking on a number of levels.
Despite the fact that words like "unpleasant" and "grating" are often used to explain the sound of dissonance, in fact all music with a harmonic or tonal basis--even music which is perceived as generally harmonious--incorporates some degree of dissonance. The buildup and release of tension (dissonance and resolution), which can occur on every level from the subtle to the crass, is to a great degree responsible for what many listeners perceive as beauty, emotion, and expressiveness in music.
Dissonance and musical style
Understanding a particular musical style's treatment of dissonance--what is considered dissonant and what rules or procedures govern how dissonant intervals, chords, or notes are treated--is key in understanding that particular style. For instance, in the common practice period, harmony is generally governed by chords, which are collections of notes generally considered to be consonant (though even within this harmonic system there is a hierarchy of chords, with some considered relatively more consonant and some relatively more dissonant). Any note that does not fall within the prevailing harmony is considered dissonant. Particular attention is paid to how dissonances are approached (approach by step is less jarring, approach by leap more jarring), even more to how they are resolved (almost always by step), to how they are placed within the meter and rhythm (dissonances on stronger beats are considered more forceful and those on weaker beats less vital), and to how they lie within the phrase (dissonances tend to resolve at phrase's end). In short, dissonance is not used willy-nilly but is used in a very careful, controlled, and well circumscribed way. The subtle interplay of different levels of dissonance and resolution is vital to understanding the tonal and harmonic language of this period.
Dissonance throughout the history of western music
Dissonance has been understood and heard differently in different musical traditions, cultures, styles, and time periods.
In early Renaissance music intervals such as the perfect fourth and thirds were considered strong dissonances that must be immediately resolved. The regola delle terze e seste ("rule of sixths and thirds") required that imperfect consonances should resolve to a perfect one by a half step progression in one voice and a whole step progression in another (Dahlhaus 1990, p.179). Anonymous 13 allowed two or three, the Optima intorductio three or four, and Anonymous 11 (15th century) four or five successive imperfect consonances. By the end of the 15th century imperfect consonances where no longer "tension sonorities" but, as evidence by the allowance of their successions argued for by Adam von Fulda, but independent sonorities, according to Gerbert (vol.3, p.353), "Although older scholars once would forbid all sequences of more than three or four imperfect consonances, we who are more modern allow them." (ibid, p.92)
In the common practice period dissonant melodic intervals include the tritone and all augmented and diminished intervals. Dissonant harmonic intervals include:
Thus, Western musical history can be seen as starting with a quite limited definition of consonance and progressing towards an ever wider definition of consonance. Early in history, only intervals low in the overtone series were considered consonant. As time progressed, intervals ever higher on the overtone series were considered consonant. The final result of this was the so-called "emancipation of the dissonance" (the words of Arnold Schoenberg) by some 20th-century composers. Early 20th-century American composer Henry Cowell viewed tone clusters as the use of higher and higher overtones.
Despite the fact that this idea of the historical progression towards the acceptance of ever greater levels of dissonance is somewhat oversimplified and glosses over a great number important developments in the history of western music, the general idea was attractive to many 20th-century modernist composers and is considered a formative meta-narrative of musical modernism.
Melodic versus harmonic dissonance
There is also a distinction between melodic and harmonic dissonance. For instance, a minor second is highly dissonant harmonically but not melodically, while the tritone is often considered a harmonic and melodic dissonance. Dissonances were required to be beat oscillations, which are caused when the two pitches cause interference, or reinforce and cancel each others amplitudes. Most listeners experience these beat oscillations and interference as a roughness in the sound that is unpleasant or dissonant. The roughness increases to a certain point as frequencies of the two pitches become closer together, reaching a high point of roughness, then decreasing as the frequencies become perceptually indistinguishable.
- Ogg Vorbis audio file of two pitches moving the interval of a Major 2nd to a unison, illustrating roughness and beat oscillations that gradually reduce as the interval moves towards the unison.
- Frequency ratios: ratios of higher simple numbers are more dissonant than those which are lower (Pythagoras).
- Ogg Vorbis audio file of the two diverging sinusoidal-like tones - the sinusoidal-like tones are filtered triangle waves, which have strong fundamentals, no even overtones (at 2x, 4x, 6x, etc. the fundamental frequency) and highly attenuated odd overtones (at 3x, 5x, 7x, etc. the frequency).
- Ogg Vorbis audio file of the two diverging tones with sawtooth waveform--the sawtooth wave has strong overtones, both even and odd, which make some points of dissonance and consonance more audible.
The physical basis for Pythagoras's observation can be seen in the spectral analysis above and heard in the accompanying sound file. At the points where the ratios of the frequencies of the tones are more simple (indicated by arrows near the top of the graph), the overtones as observed in the spectral analysis are more ordered and simple. Most listeners perceive the tone of the interval at these points to be more "pure" or "harmonious".
By contrast, when the ratios of the frequences are not simple, the overtone situation appears complex and chaotic in the spectral analysis. Most listeners perceive the intervals at these points to be "rougher" or more "disharmonious".
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In human hearing, the varying effect of these different ratios may be perceived by one of these mechanisms:
- Fusion or pattern matching: fundamentals may be perceived through pattern-matching of the separately analyzed partials to a best-fit exact-harmonic template (Gerson & Goldstein, 1978) or the best-fit subharmonic (Terhardt, 1974) or harmonics may be perceptually fused into one entity, with dissonances being those intervals which are less likely to be mistaken for unisons, the imperfect intervals, because of the multiple estimates, at perfect intervals, of fundamentals, for one harmonic tone (Terhardt, 1974). By these definitions inharmonic partials of otherwise harmonic spectra are usually processed separately (Hartmann et al., 1990), unless frequency or amplitude modulated coherently with the harmonic partials (McAdams, 1983). For some of these definitions neural-firing supplies the data for pattern-matching, see directly below (e.g., Moore, 1989; pp.183-187; Srulovicz & Goldstein, 1983).
- Period length or neural-firing coincidence: with the length of periodic neural-firing created by two or more wave-forms, higher simple numbers creating longer periods or lesser coincidence of neural-firing and thus dissonance (Patternson, 1986; Boomsliter & Creel, 1961; Meyer, 1898; Roederer, 1973, p.145-149). Pure tones cause neural-firing exactly with the period or some multiple of the pure tone.
- Dissonance is also then defined by the amount of beating between non-common harmonics or partials (collectively overtones) (Helmholtz, 1877/1954). Terhardt (1984) calls this "sensory dissonance". By this definition dissonance is dependent not only on the quality of the interval between two notes, but the harmonics and thus sound quality (timbre) of those notes themselves.
- Dissonances are pitches that fall within each others critical bands.
The strongest homophonic (harmonic) cadence, the authentic cadence, dominant to tonic (D-T or V7-I), is in part created by the dissonant tritone created by the seventh, also dissonant, in the dominant seventh chord which precedes the tonic.
See also consonance.
See also
Source
- Burns, Edward M. (1999). “Intervals, Scales, and Tuning”, The Psychology of Music second edition. Deutsch, Diana, ed. San Diego: Academic Press. ISBN 0122135644.
- Dahlhaus, Carl. Gjerdingen, Robert O. trans. (1990). Studies in the Origin of Harmonic Tonality. Princeton University Press. ISBN 0691091358.
