Upright and grand pianos normally have three pedals which serve various purposes:
The left pedal on an upright piano is known as the half-blow or soft pedal. It moves the hammers closer to the strings so that they hit them with less velocity – allowing the player to produce a sound which is a little quieter and softer.
On a grand piano the left pedal is known as the una corda (one string) or shift pedal, and moves the whole piano action including the keyboard slightly to the right. The result is that the hammer strikes fewer strings per note, making the sound quieter and changing its timbre.
This is known as the damper or sustain pedal and does the same job on both upright and grand pianos. When the pedal is depressed the dampers lift off each string simultaneously, allowing the notes to sustain.
Third (centre) pedal
Upright pianos sometimes have a third pedal known as the celeste or muffler pedal which moves a thin piece of felt between the hammers and the strings in order to soften and quieten the sound. This pedal might otherwise activate a Silent System, so that the pianist can ‘switch off’ the acoustic part of the piano and simply put on some headphones or listen to the piano through some speakers. On larger Yamaha uprights including U3, YUS, and SE models the centre pedal acts as a ‘sostenuto’.
The centre pedal on a grand piano is called a ‘sostenuto’. This pedal raises only the dampers of any notes depressed before the pedal is activated, thus enabling selective sustain. It can be very useful for keeping bass notes sustained when playing complex music – it is considered essential when playing Debussy’s ‘Clair de lune’, or Rachmaninoff’s ‘Prelude in C# minor’.