Organ mass

The French Organ Mass is a type of Low Mass that came into use during the Baroque era. Essentially it is a Low Mass with organ music playing throughout: part of the so-called alternatim practice.

The French Organ Mass is a classic example of the so-called alternatim practice, a term which indicates a type of liturgy when alternate sections of liturgical items (such as a Mass or a Magnificat) were performed by different forces. In organ alternatim practice—and so, in the French Organ Mass—the organist plays when texts would otherwise have been sung. The tradition stemmed from the antiphonal psalmody of the early Western church. In France, organ playing was regulated by printed "ceremonials", which specified precisely when the organist should play. The surviving ceremonials are all similar in outline, but differ widely in details. A typical organ Mass comprised versets for the ordinary of the Mass except for the Credo (which was to be sung in its entirety).

One of the most important extant ceremonials was written in 1662 and regulated the diocese of Paris. According to this ceremonial, the organ begins the Kyrie and alternates with the choir through ninefold repetitions (and so ends the Kyrie as well). After the priest intones the first line of the Gloria, the organ again begins the alternation with the choir. After the final verse of the Gloria (which began at "in gloria Dei Patri") the organist would accompany the Offertory: this time there is no alternation and the music does not replace the chant as earlier (while there are texts for the Offertory, they are not for the choir). After the Offertory comes the Sanctus, followed by the Elevation, a high point in the liturgy. The Sanctus begins with an organ verse and proceeds in any of the following three ways:

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