Стандарт высоты тона Ля 440 Гц

Pitch standard

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 International Organization for Standardization 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.

Before standardization on 440 Hz, many countries and organizations followed the French standard since the 1860s of 435 Hz, which had also been the Austrian government's 1885 recommendation. Johann Heinrich Scheibler 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 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 keyboard. On MIDI, A440 is note 69 (0x45 hexadecimal).

A440 is widely used as concert pitch in the United Kingdom and the United States. In continental Europe the frequency of A4 commonly varies between 440 Hz and 444 Hz. known as Chorton pitch at 466 Hz (with 440 Hz corresponding to A), and classical pitch at 427–430 Hz.