Piano pedals

Piano pedals are foot-operated levers at the base of a piano which change the instrument's sound in various ways. Modern pianos usually have three pedals, from left to right, the soft pedal (or una corda), the sostenuto pedal, and the sustaining pedal (or damper pedal). Some pianos omit the sostenuto pedal, or have a middle pedal with a different purpose such as a muting function also known as silent piano.

The development of the piano's pedals is an evolution that began from the very earliest days of the piano, and continued through the late 19th century. Throughout the years, the piano had as few as one modifying stop, and as many as six or more, before finally arriving at its current configuration of three.

The damper pedal, sometimes called the sustaining pedal, is used more often than the other pedals, and is placed at the right of the array of pedals, most conveniently accessible to (mostly right-footed) players. The damper pedal raises all the dampers off the strings so that they keep vibrating after a key on the keyboard has been released. In effect, the damper pedal makes every string on the piano a sympathetic string, creating a rich tonal quality; it is probably this effect that lies behind the common saying that the damper pedal is "the soul of the piano". The damper pedal has the secondary function of allowing the player to connect into a legato texture notes that otherwise could not thus be played.

The una corda mechanism, invented by Bartolomeo Cristofori, was the first stop invented to modify the piano's sound. This function is typically operated by the left pedal on modern pianos. The common name many use today for the una corda is the soft pedal. Neither name is an entirely accurate description of the pedal's function. The una corda primarily modifies the timbre, not just the volume of the tone.

Soon after its invention, the una corda was integrated on pianos of all makers as a standard fixture. On Cristofori's pianos, the una corda mechanism was operated by a hand stop, not a pedal. The stop was a knob on the side of the keyboard. When the una corda was activated, the entire action shifted to the right so that the hammers hit one string (una corda) instead of two strings (due corde).

...
Wikipedia