'Continuous Glissando' or Portamento
Musical instruments with continuously variable pitch can effect a portamento over a substantial range. These include unfretted stringed instruments (such as the violin, viola, cello and double bass, and fretless guitars), stringed instruments with a way of stretching the strings (such as the guitar, veena, or sitar), a fretted guitar or lap steel guitar when accompanied with the use of a slide, wind instruments without valves or stops (such as the trombone or slide whistle), timpani (kettledrums), electronic instruments (such as the theremin, the ondes martenot, synthesizers and keytars), the water organ, and the human voice. The musical saw, or "singing saw", plays entirely in a portamento.
Portamenti can be produced over a limited range on most instruments; for example, fretted stringed instruments (such as the guitar or mandolin) can effect a portamento by pushing the string across the fingerboard. This is commonly called note bending rather than a portamento.
Brass and woodwind instruments such as the trumpet or flute can effect a similar limited slide by altering the lip pressure (trumpet) or a combination of embouchure and rolling the head joint (flute), while the clarinet and some models of flute can achieve this by slowly dragging fingers off tone holes while adjusting the embouchure. The trombone is especially conducive to producing portamenti of up to an augmented fourth, though the effect is limited by the slide position and partial of both notes involved.
Tunable percussion instruments such as the drum or conga can effect this by applying or releasing pressure on the head while striking.
Many electric guitars are fitted with a tremolo arm which can produce either a portamento, a vibrato, or a combination of both (but not a true tremolo despite the name). By pressing the arm towards the body of the guitar, the guitarist moves the bridge of the guitar both away from the body and forward (towards the headstock), thereby decreasing string tension and lowering the pitch any notes that are sounding. This technique can often produce portamenti of incredible range, with the guitarist often being able to reduce tension to the point that the strings become slack. Such a portamento however is rarely used to melodic effect, instead being implemented as a special effect; however, some guitarists (most notably Jimi Hendrix, Steve Vai, and Joe Satriani) have strongly focused on the use of extended portamenti for melodic effect. Some guitars feature a vibrato that is also capable of being pulled away from the guitar body, resulting in an increase in string tension and therefore an increase in pitch. Extended use of portamento figures on guitars without locking nuts can cause the strings to be pulled out of tune.
Portamento can often be generated automatically on synthesizers, where a parameter setting can be used to control the speed at which an oscillator moves to a new pitch. Often this parameter is called glide. Alternatively, portamento effects can be produced manually by a skilled player through the use of the pitch bend wheel at the side of many synthesizer keyboards, or alternatively by means of a ribbon controller. Synth lines with lots of portamento defined West Coast G funk of the mid 1990s, and continue to be a distinctive part of electronic music today, as well as progressive rock music (see Dream Theater's Jordan Rudess.)
In MIDI sequencing, portamento can be generated by using a channel message that creates a sliding effect by smoothly changing pitch from the last note played to the pitch of the currently playing note.
The Casio CZ-101 was one of the first synthesizers to have a polyphonic portamento effect.
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