What Does the Middle Pedal on a Piano Do?

If you play the piano even casually, you probably know that the sustain pedal on the right makes all the notes you play hold until you release the pedal. The other 2 piano pedals are not as clear cut. In fact, only the sustain pedal operates on upright pianos. The other pedals do various things, but seldom what they are designed to do. Even some grand pianos pedals don’t operate the way they are intended.

The left pedal, sometimes referred to as the soft pedal is actually called the une corde pedal for “one string”. Indeed, early pianos had 2 strings for each note and the une corde pedal shifted the action so that the hammers only struck one string. Modern pianos have 3 strings for each note throughout most of the piano. So the une corde pedal shifts the action so that the hammers strike only 2 of the strings squarely. This is significant because it not only makes the notes quieter, but if offers a change of timbre. Upright pianos usually offer a soft pedal that changes the feel, not the sound. It does this by shifting the hammers closer to the strings making it harder to play loud.

The middle pedal is seldom used and even more seldom understood. Most pianos didn’t have functioning sostenuto pedals as they are called until the end of the 19th century. Many European piano manufacturers didn’t include middle piano pedals until well into the 20th century. Like the sustain pedal, the sostenuto pedal holds notes after you release the keys. The difference is that subsequent notes that are depressed will not hold, only the notes that were depressed when the middle pedal is engaged. This is useful in a few scores of Debussy and other 20th century composers. It’s like having a 3rd hand to hold notes in another register without blurring the harmonies with the sustain pedal. However, the sostenuto pedal is only called upon in 20th century music and very few compositions. It is by no means essential but could be important for someone specializing in 20th century piano music.