The organ's bold, unwavering tones provide excellent
support for hymn singing and the perfect medium for a wide variety
of organ literature. In some music, however, the addition of a subtle,
wave-like motion, especially to long notes, can assist the projection
of musical line and enhance the appeal of the music. For this reason
the tremulant has been part of organ design for hundreds of years.
The tremulant is a device that causes an undulation (flexibility)
in the wind supplied to the pipes. This device, built into the wind
line, changes the wind pressure in a repeating cycle.