Organ

   The most important traditional instrument in Christian music, also known in some kinds of non-Orthodox Jewish music, and the Hindu bhajan, the term refers to a family of keyboard instruments derivative of the pipe organ. Members of one branch of the family produce sound by forcing air through a set of scaled vibrators activated by the keyboard: pipes of different lengths, materials, and shapes in pipe organs, portatives, and positives; vibrating metal tongues of different lengths in harmoniums and regals. Members of a second branch attempt to imitate the sound of a pipe organ by producing sound through loudspeakers controlled either by oscillators of varying frequencies as in the early 20th-century electronic organ, or by sound samples stored in computers as in the late 20th-century digital organ.

   "Organ" therefore will denote different instruments depending upon the context. Discussions of historical repertory (e.g., "the organ music of Johann Sebastian Bach"), refer almost certainly and exclusively to pipe organ, but in a performance of an oratorio it could well be the positive, and reference to "the organ" in a modern church could denote a pipe organ, a positive, an electronic organ, or a digital organ.

   As the sole instrument admitted to Christian liturgies since the 10th century, the organ has by far the largest and most varied repertory of sacred instrumental music, and has in those centuries acquired an incomparable connotation of the sacred for Western culture. Nevertheless, the tradition of organ playing has declined noticeably in the last half of the 20th century owing to the use of popular styles in the gospel songs and praise choruses common in Evangelical Protestantism throughout the century and in folk masses in Roman Catholicism since the Second Vatican Council.