A trumpet voluntary is a classical, English-based musical composition that was especially popular during the Baroque period. Although the term "trumpet voluntary" conjures the idea that a trumpet performs the works, these compositions technically are for a solo keyboard instrument. The name comes from the fact that originally, the works generally were performed by organists utilizing the organ's trumpet stop.
By definition, it is not a religious piece of music, but organists used the pieces with high frequency before, during and after religious services. The works essentially were "filler" music that were not part of the regular service. The use of the voluntary in this function did not mean the work was of insignificant quality. Many are masterpieces in their own right and were selected for use specifically because the organist felt the musicality of the compositions made them deserving of performance.
There is no set form for these compositions because it was how the works were performed — with the trumpet stop before, during or after a service — that truly designated whether they fit the voluntary definition, not the form of the work. It is fairly standard, however, for a trumpet voluntary to start with a slower tempo. Once the performer has played this slower introduction, the tempo usually changes to a faster speed. The left hand usually plays an accompanying chord pattern or theme, with the right hand providing a fanfare.
Another reason why no set form for a trumpet voluntary exists is that organists usually improvised the works. Good organists did not find this especially difficult to do, because they had been trained in theory and counterpoint. This is an important fact, because it draws a clear line between "true practice" voluntaries and the ones that have become famous because they were written down and now are performed according to what is present on the music page.
When musicians had a written version of a voluntary they liked, they quickly made arrangements of it to suit their own instruments. This allowed the voluntary to move out of the church setting and into homes as entertainment music. Eventually, trumpet voluntaries made their way into concert halls and onto professional studio recordings.
Out of all the compositions labeled as a trumpet voluntary, perhaps the most famous is the "Prince of Denmark March." Contemporary musicians also know this work loosely as the "Trumpet Voluntary in D," although it is certainly not the only voluntary in that key. This work, composed by Jeremiah Clarke and misattributed for years to Henry Purcell, is used with regularity for weddings worldwide. It was a selection in the wedding of Prince Charles and Lady Diana Spencer of England.