In music, a glissando (plural: glissandi, abbreviated gliss.) is a glide from one pitch to another. It is an Italianized musical term derived from the French glisser, to glide. In some contexts it is distinguished from the continuous portamento. Some colloquial equivalents are slide, sweep (referring to the 'discreet glissando' effects on guitar & harp respectively), bend, slide, or 'smear'.
Glissando vs. portamento
Prescriptive attempts to distinguish the glissando from the portamento by limiting the former to the filling in of discrete intermediate pitches on instruments like the piano, harp and fretted strings have run up against established usage of instruments like the trombone and timpani. The latter could thus be thought of as capable of either 'glissando' or 'portamento', depending on whether the drum was rolled or not. The clarinet gesture that opens Rhapsody in Blue could likewise be thought of either way, being originally for piano, but is in practice played as a portamento and described as a glissando. In cases where the destination and goal pitches are reduced to starting and stopping points as in James Tenney's Cellogram, or points of inflection, as in the sirens of Varèse's Hyperprism, the term portamento (conjuring a decorative effect) seems hardly adequate for what is a sonorous object in its own right and these are called glissando.
On some instruments (e.g., piano, harp, xylophone), discrete tones are clearly audible when sliding. For example, on a keyboard, the player can slide his or her fingertips across the white keys or their fingers over the black keys, producing either a C major scale or an F# major pentatonic (or their relative modes); or, by performing both at once, it is possible to produce a full chromatic scale, but this is difficult. On a harp, the player can slide his/her finger across the strings, quickly playing the scale (or on pedal harp even arpeggios such as C♭-D-E♯-F-G♯-A♭-B). Wind, brass and fretted stringed instrument players can effect an extremely rapid chromatic scale (ex: sliding up or down a string quickly on a fretted instrument). Arpeggio effects (likewise named glissando) are also obtained on the harmonic series by bowed strings and brass, especially the horn.
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