음정 주파수 계산기 (Hz)

계산 원리

This is twelve-tone equal temperament, computed as f = A4 × 2^((MIDI − 69) ÷ 12). The MIDI number comes from (octave + 1) × 12 plus the semitone index, which puts middle C at 60 and A4 at 69, the scientific pitch convention. Cents are applied as a second factor of 2^(cents ÷ 1200). Alongside the frequency you get the note name with its octave, the MIDI number, and the period in milliseconds as 1000 divided by the frequency.

The A4 reference field is the input that moves everything, accepting 400 to 500 Hz in hundredths with preset buttons for 432, 440, 442 and 444 Hz. Because the whole scale is derived from it, dropping A4 from 440 to 432 lowers every note by about 31.8 cents. Octave selection spans 0 to 9 in scientific notation, and the cents slider offers plus or minus 100 — a full semitone in either direction — for checking detune amounts.

Equal temperament is a compromise, and this calculator implements only that. It has no just intonation, no historical temperaments, and no stretch tuning, so it will not match a real piano, whose octaves are deliberately widened to suit string inharmonicity. The cents slider affects only the large readout; the twelve rows in the table are always calculated at zero cents. The octave list also runs past the MIDI specification, since anything above G9 produces numbers beyond the valid 0 to 127 range.

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