Contrary to wind or string instruments a glissando on the harp is not a gradual pitch glissando. (For a gradual glissando see Tuning key slide.) Similar to the piano the effect is produced by sliding the fingers quickly over the strings to create a fast scale. Unlike the piano, however, the harp can produce glissandi that sound like a chord or cluster by setting the pedals in different positions. This is unique to the harp and is probably the reason why glissandi have been immensely popular on the pedal harp.