Sustain pedal
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A sustain or sustaining pedal (also damper pedal or loud pedal) is the most commonly-used pedal in a modern piano. It is typically the rightmost of two or three pedals. When pressed the sustain pedal "sustains" all the strings on the piano, removing the dampers from all strings and allowing them to vibrate freely. This serves two purposes. First, it assists the pianist in producing a legato (playing smoothly connected notes) in passages where no fingering is available to make this otherwise possible. Secondly, raising the damper pedal causes all the strings to vibrate sympathetically with whichever notes are being played, which greatly enriches the piano's tone.
The sostenuto pedal, in contrast, sustains only notes which are depressed at the time the pedal is depressed.
Vibraphones also have sustain pedals that allow the metal bars to ring.
The use of the pedal is often a matter of discretion to the musician, but there is special notation when the composer wishes to specify it. The most common is the use of a horizontal line below the grand staff, which lifts up and down with the pedal. An alternative notation is 
where the pedal is supposed to be depressed, and * to show where it should be lifted.
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