The role of the organ

The 1801 brief for the construction of the new Chapel mentioned ‘an Organ for Cathedral Service’. This refers to the principal function of the Chapel organ, which was to accompany the choir's singing of the musical parts of the choral service. The primacy of this function of the organ in English choral foundations is emphasized by John Jebb:

In an era in which choirs were not conducted during church services, the choir was not merely accompanied by the organ, but led and directed by its sound, according to the interpretation of the organist. The organist was thus the superintendent of the entire musical service, for his playing shaped the singing. The distinctive sound of the organ, and the way in which the organist chose sonorities for accompaniment, would have affected the quality of the choir's singing. Thus, the combination of choir and organ resonating in the Chapel's peculiar dry acoustic would have created a distinctive sound-world for the worshippers who attended services at the Chapel.

Besides its principal use in accompanying the choir, the organ may have been used to provide ‘voluntaries’ – a term given to solo organ music, either composed or improvised, that accompanied liturgical action. Nowadays, the term ‘voluntary’ usually refers to a piece of organ music played at the conclusion of a service, but in past times there existed the tradition of the ‘middle voluntary’, which was played after the chanting of the psalm and before the reading of the first lesson in Morning and Evening Prayer:

Jebb noted that this practice had ceased shortly before the time of writing (1843) in the Dublin cathedrals, but did not mention whether or not this middle voluntary was used in the Chapel Royal. According to Jebb, this voluntary ‘should be a short, slow movement, chiefly upon the diapasons and unisons’, and that ‘all shewy gavots, and noisy trumpet pieces’ should be avoided.