Glissando

In music, a glissando [ɡlisˈsando] (plural: glissandi, abbreviated gliss.) is a 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 portamento. Some colloquial equivalents are slide, sweep (referring to the 'discrete glissando' effects on guitar & harp respectively), bend, smear, rip (for a loud, violent gliss to the beginning of a note),lip (in jazz terminology, when executed by changing one's embouchure on a wind instrument), or falling hail (a glissando on a harp using the back of the fingernails).

From the standpoint of musical acoustics and scientific terminology, some instruments, such as slide trombones, unfretted bowed-string instruments, guitars played with slides and, of course, slide whistles, can change the frequency of their notes continuously, while others, notably acoustic keyboard instruments, are restricted to quantized (stepped) changes in pitch. (The clavichord's Bebung is the one exception, but that is essentially ornamentation of a single pitch, not a glide.) Some instruments, such as the clarinet and saxophone, can produce a continuous pitch (frequency) change, although their characteristic design is to provide distinct pitches.

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 stringed instruments 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: it was originally planned as a glissando (Gershwin's score labels each individual note) but is in practice played as a portamento though described as a glissando.

On some instruments (e.g., piano, harp, xylophone), discrete tones are clearly audible when sliding. For example, on a keyboard, a player's fingertips can be made to slide across the white keys or 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 their 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 perform an extremely rapid chromatic scale (e.g., sliding up or down a string quickly on a fretted instrument).

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