Three Pedals on the Grand
There are three pedals on the grand piano – they are named, from left to right, the una corda, sostenuto, and damper pedal. The purpose of the pedals is to change the tone of the piano in some way.
The damper pedal, also called the sustain pedal, prolongs the sound of the piano by lifting all of the dampers off the strings. This sustains the sound, and also allows all of the strings to vibrate sympathetically.
The sostenuto pedal acts as a selective damper – when the pedal is activated, the sostenuto rod engages and holds up only those dampers that have been raised by their keys. The dampers that are at rest remain unaffected. This sustains only the notes that are depressed when the pedal is activated.
The una corda thins the tone of the piano by shifting the entire keyboard and action slightly to the right so that the hammers do not strike all of the strings. The shifting of the action also allows the hammers to strike the string with a different portion of the hammer head. Over time, the felt of the hammer head can become compacted from repeatedly striking the strings. When the keyboard is shifted, the hammers strike the strings with a different, softer portion of the hammer head, which affects the sound.