What is the role of the 'una corda' pedal on the piano?

The 'una corda' pedal plays a significant role in altering the sound produced by the piano. When this pedal is engaged, it shifts the piano action so that the hammers strike only one of the three strings (or two strings for certain notes) instead of all three. This results in a softer, more delicate tone, creating a subtler sound compared to when the pedal is not used. The purpose of this pedal is primarily to soften the overall dynamic of the music, allowing for expressive playing particularly in quieter passages.

This contrasts with the function of the other pedals; for instance, the sustain pedal enhances volume by allowing notes to resonate after they are played, while the timing of notes is not controlled in any way by the una corda pedal. Additionally, the pitch stability is not impacted through this pedal, as it does not affect the tuning but rather modifies the tonal quality. Therefore, the primary and defining characteristic of the 'una corda' pedal is its ability to soften the sound.