The pipes come in various keys. The most popular being
the key of D (The D above middle C on the piano i.e. Concert pitch) These
were developed in the 1920`s by the Taylor Brothers in Chicago who
needed pipes which were louder and could play in ensembles. The previous
pipes made were for solo playing and were in the keys of C
Composers need to be aware of the properties of the pipes.
I have gone to recording sessions in well-known London studios where famous
and expensive film composers have written music incorporating the pipes
only to find that what was written, was virtually impossible to play!