Ask the Piano Lady

Curious in Cambridge wrote: "I don't have a piano but here's something I've wondered for a long time: why do some pianos have two pedals and other pianos have three? What do the pedals do?"

Dear Curious: The modern piano, which has been around since about 1850, originally had only two pedals. The one on the right is the damper lift pedal or the "loud pedal" and the one on the left is the "una corda" or soft pedal. The dampers are blocks of felt that normally sit on the piano strings to stop them from making noise. In music it is just as important to stop the sound as it is to start it. When an individual piano key is played there is a tab or "spoon" that lifts the damper for each string and then it goes back into place (resting on the string) when your finger is lifted off the key. The damper pedal, usually activated by the right foot, lifts all of the dampers at once allowing a pleasant wash of sound to spill forth from the piano. It makes the piano seem louder. The "una corda" or soft pedal on a grand piano actually moves the entire keyboard to the right so that the hammers are realigned to hit only 2 of the 3 strings thus making a softer sound. On an upright piano the keyboard does not shift, but the left pedal actually moves the entire set of hammers closer to the strings so that the hammers travel a shorter distance to the string, not picking up as much speed as normal, thus producing a softer sound. The third pedal (in the middle) is largely something that was added by North American piano manufacturers. Many European pianos still have only 2 pedals. Traditionally, the middle pedal on a grand piano (and some uprights) is called the "sostenuto" which means sustaining. The sostenuto pedal, when depressed, will hold up only one or a few dampers, as indicated by the music, while other notes can be played and will not be sustained. It is like a "dim sum" damper pedal - you can choose which of the notes will be sustained and which not. (I have played the piano most of my life and have only ever used the sostenuto in one piece by Rachmaninoff because my hands are not big enough to span the notes he wrote.) Throughout its evolution the piano has had as many as eight pedals all producing some kind of special effect: some were used to activate percussion instruments that were added to the piano; on other instruments the third pedal lowered leather strips with little metallic buttons so that the piano would sound like a “honky-tonk”.