Middle C
In terms of musical pitch, C or Do is the first note of the fixed-Do solfège scale. When the A440 pitch standard is used to tune a musical instrument, Middle C has a frequency around 261.6 Hz. Middle C is designated C4 in scientific pitch notation because of the note's position as the fourth C key on a standard 88-key piano keyboard. Another system known as scientific pitch assigns a frequency of 256 Hz but, while numerically convenient, this is not used by orchestras. Other note-octave systems, including those used by some makers of digital music keyboards, may refer to Middle C differently. In MIDI, Middle C is note number 60.