There are many pieces throughout the history of organ literature in which the pedal uses a solo stop to play the melody. Couplers Couplers allow stops from different divisions to be played by a single manual. It is similar to a copy command in a word processing program. For more on couplers, see A Closer Look at the Console . The choice of stops and couplers which the organist uses in a piece of music is the registration.
Some composers specify the stops to be used.
If the organ does not have the same exact stop names that the composer wants, the organist substitutes a similar stop. Open Diapason, an 8' Montre can be substituted. The Montre does have a different tonal quality than the Open Diapason but they are close enough so that the musical effect is still close to what the composer wanted. However, substitution does not always work well. Some organ works use so many stops that they can only be played on large organs.