Sébastien Erard (1752 - 1831) was a French instrument maker who specialised in the production of pianos and harps, in his Paris and London factories. Erard developed the capacities of both instruments.
Invented around 1823, his piano "double escapement" action is essentially the same as in modern pianos. This allows individual notes to be rapidly repeated.
His "double movement" pedal action for the harp (invented around 1810) allows each string to be shortened by a semitone (half-step) or two semitones, creating a whole tone. Earlier systems were single action, where a string could only be shortened a semitone, limiting the playable keys. This mechanism allows a harpist to perform in any key or chromatic setting.
