Harp strings have an assigned pitch. For example, all the red strings are "C" strings, and all the black/blue strings are "F" strings. In order to change the pitch without tuning, a harpist uses either levers or pedals.
Lever harps have a small lever for each string, and when the harpist raises the lever of a string, it raises the pitch by a half step. For example, when a lever is raised, a "C" string becomes "C-sharp." Each string has to be changed individually with the harpist's left hand. That means that if there is a key change or accidental in the middle of a piece, the left hand has to stop playing in order to change the strings' pitches. It also means that a lever harp can only play in certain keys, as each string can either be sharp and natural, or natural and flat, depending on the tuning.
On the pedal harp, each group of pitches has an assigned pedal with 3 positions. For example, if the "C" pedal is in the top position, every "C" string will be a "C-flat." If the pedal is in the middle position, all the "C" strings will be "C-natural." When the pedal is in the bottom position, all the "C" strings will be "C-sharp." This means that a harpist can continue playing with both hands when a key change or accidental is needed, because the pedals are changed by the harpist's feet. It also means that a harpist can play in any key, because all of the strings can be made sharp, flat, or natural.
Other differences between pedal and lever harps include the number of strings and the size of the instrument. Pedal harps are larger than lever harps, often at least 6 feet tall. Their larger size means that they can fit more strings - up to 47. Lever harps are around 5 feet tall and average around 36 strings.
