A reference pitch has two functions:
(1) It serves as a point of commonality among different instruments
(2) It is the first note one tunes before setting the temperament of a keyboard instrument, the note from which all other notes are tuned, either directly or by a series of intervals
In the environment of Equal Temperament and fully chromatic modern wind instruments, the identity of the reference note is of no importance. The modern use of A is an expedient which allows all the strings of the orchestra to tune from a single note given by the oboe, since A is the highest-string note common to all instruments (on instruments with constant string length, the higher the note the higher the extension of the material, meaning more pitch stability under bowing pressure and atmospheric changes). However, the situation has not always been so, and there are many good reasons to return to a historical practice when using unequal temperaments and historical instruments.
These pages are intended to provide information about historical reference pitch practice as well as to explain why returning to historical practice is important for HIPP musicians.