Harp

The harp belongs to the string family in the broad sense — it makes sound from vibrating strings — but works quite differently from the bowed instruments around it. Its strings run vertically and are plucked directly with the fingers, and pitch is changed not by pressing strings against a fingerboard but by pressing one of seven foot pedals, each of which can raise a whole set of same-lettered strings by a half or whole step.

That pedal mechanism makes the harp less harmonically flexible in fast passages than a keyboard instrument, which is part of why composers tend to use it sparingly and specifically — for shimmering arpeggios, delicate accompaniment, or a distinctive splash of color — rather than as a constant presence the way strings or woodwinds are used.

The modern orchestral (or "pedal") harp, with its full chromatic pedal system, was developed in the early 1800s; earlier harps, including many folk harp traditions still played today, use simpler tuning systems without that pedal mechanism.

Where to start listening: the harp glissando (a rapid sweep across the strings) that opens Tchaikovsky's Waltz of the Flowers is one of the instrument's most recognizable orchestral moments.