International Concert Pitch
In 1939, an international conference recommended that the A above middle C be tuned to 440 Hz, now a standard known as International Concert Pitch. This standard was taken up by the International Organization for Standardization in 1955 (and was reaffirmed by them in 1975) as ISO 16. The initial standard was A = 439 Hz, but this was superseded by A = 440 Hz after complaints that 439 Hz was difficult to reproduce in a laboratory owing to 439 being a prime number.
The French standard for A4 at 435 Hz, the diapason normal, should be measured at 15°C, and a change to 20°C causes a shift to very nearly 440 Hz.
- William Vennard (1967). “Pitch”, Singing: The Mechanism and the Technic, 5th ed. Carl Fischer, LLC, p. 3. ISBN 0825800552.
- ISO 16:1975; Acoustics -- Standard tuning frequency (Standard musical pitch). ISO Standards. Retrieved on 2012-07-05.
- Lynn Cavanagh. A brief history of the establishment of international standard pitch a=440 hertz (PDF). WAM: Webzin o audiju i muzici. Retrieved on 2012-06-27.
- George Ashdown Audsley (1965). The Art of Organ-building: A Comprehensive Historical, Theoretical, and Practical Treatise on the Tonal Appointment and Mechanical Construction of Concert-room, Church, and Chamber Organs, Volume 2, Reprint of 1905 ed. Courier Dover Publications, p. 636. ISBN 0486213153.