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A440 (also known as Stuttgart pitch) is the musical pitch corresponding to an audio frequency of 440 Hz, which serves as a tuning standard for the musical note of A above middle C, or A4 in scientific pitch notation. It is standardized by the
A440 is widely used as concert pitch in the
International Organization for Standardization
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...
as ISO 16. While other frequencies have been (and occasionally still are) used to tune the first A above middle C, A440 is now commonly used as a reference frequency to calibrate acoustic equipment and to tune pianos, violins, and other musical instruments.
History and use
Before standardization on 440 Hz, many countries and organizations followed the French standard since the 1860s of 435 Hz, which had also been theAustria
Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
n government's 1885 recommendation. Johann Heinrich Scheibler
Johann Heinrich Scheibler (11 November 1777 – 20 January 1837) was a silk manufacturer from Crefeld, Prussia, without a scientific background, who went on to make contributions to the science of acoustics as a self taught musicologist. He made ...
recommended A440 as a standard in 1834 after inventing the "tonometer" to measure pitch, and it was approved by the Society of German Natural Scientists and Physicians at a meeting in Stuttgart the same year.
The American music industry reached an informal standard of 440 Hz in 1926, and some began using it in instrument manufacturing.
In 1936, the American Standards Association recommended that the A above middle C be tuned to 440 Hz. This standard was taken up by the International Organization for Standardization
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...
in 1955 as Recommendation R 16, before being formalised in 1975 as ISO 16.
It is designated A4 in scientific pitch notation because it occurs in the octave that starts with the fourth C key on a standard 88-key piano
The piano is a stringed keyboard instrument in which the strings are struck by wooden hammers that are coated with a softer material (modern hammers are covered with dense wool felt; some early pianos used leather). It is played using a musica ...
keyboard. On MIDI
MIDI (; Musical Instrument Digital Interface) is a technical standard that describes a communications protocol, digital interface, and electrical connectors that connect a wide variety of electronic musical instruments, computers, an ...
, A440 is note 69 (0x45 hexadecimal
In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, h ...
).
Modern practices
A440 is widely used as concert pitch in the United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
and the United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
. In continental Europe the frequency of A4 commonly varies between 440 Hz and 444 Hz.
In the period instrument movement, a consensus has arisen around a modern ''baroque pitch'' of 415 Hz (with 440 Hz corresponding to A), a 'baroque' pitch for some special church music (in particular, some German church music, e.g. the pre-Leipzig
Leipzig ( , ; Upper Saxon: ) is the most populous city in the German state of Saxony. Leipzig's population of 605,407 inhabitants (1.1 million in the larger urban zone) as of 2021 places the city as Germany's eighth most populous, as ...
period cantatas of Bach
Johann Sebastian Bach (28 July 1750) was a German composer and musician of the late Baroque period. He is known for his orchestral music such as the ''Brandenburg Concertos''; instrumental compositions such as the Cello Suites; keyboard wo ...
)Oxford Composer Companion JS Bach, pp. 369–372. Oxford University Press, 1999 known as '' Chorton pitch'' at 466 Hz (with 440 Hz corresponding to A), and ''classical pitch'' at 427–430 Hz.
A440 is often used as a tuning reference in just intonation regardless of the fundamental note or key.
The US time and frequency station WWV broadcasts a 440 Hz signal at two minutes past every hour, with WWVH broadcasting the same tone at the first minute past every hour. This was added in 1936 to aid orchestras in tuning their instruments.
See also
* History of pitch standards in Western music * Electronic tunerReferences