A440, also known as the A above “middle C”, and further known as the note most commonly associated with 440 hertz was made the international standard for pitch decided upon in 1955 (ISO 16), and was reaffirmed by the same organization in 1975. It should also be noted that although some orchestras tune to an electronic tone that is calibrated to 440 hertz, many do not. Many orchestras are primarily concerned with whether or not they’re in tune with each other, and as such, the entire orchestra (or band) often tune to an oboe. The oboe cannot easily change its tuning, so often the other members of the orchestra to it.

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