C or Do is the first note and semitone of the C major scale, the third note of the A minor scale (the relative minor of C major), and the fourth note (G, A, B, C) of the Guidonian hand, commonly pitched around 261.63 Hz. The actual frequency has depended on historical pitch standards, and for transposing instruments a distinction is made between written and sounding or concert pitch. It has enharmonic equivalents of B♯ and D.
In English the term Do is used interchangeably with C only in the context of fixed Do solfège; in the movable Do system Do refers to the tonic of the prevailing key.
Frequency
Historically, concert pitch has varied. For an instrument in equal temperament tuned to the A440 pitch standard widely adopted in 1939, middle C has a frequency around 261.63 Hz (for other notes see piano key frequencies). Scientific pitch was originally proposed in 1713 by French physicist Joseph Sauveur and based on the numerically convenient frequency of 256 Hz for middle C, all C's being powers of two. After the A440 pitch standard was adopted...
⊥ᵒᵚ Cᵸᵎᶺᵋᶫ∸ᵒᵘ ☑️
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