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About C♯2
C♯2 / D♭2 has a frequency of 69.3 Hz in standard tuning, where A4 is fixed at 440 Hz. It is MIDI note 37 and key number 17 on an 88-key piano.
In equal temperament every semitone multiplies the frequency by the twelfth root of two (≈1.05946), so C♯2 is 32 semitones below A4: f = 440 × 2^((37 − 69) / 12) = 69.30 Hz. The number in the name is the octave in scientific pitch notation, which starts each octave on C.
C♯2 and D♭2 are enharmonic: on a piano or in equal temperament they are the same key and the same frequency, but they are spelled differently depending on the key signature.
C♯2 frequency in different tunings
| Tuning reference | C♯2 frequency |
|---|---|
| A4 = 440 Hz (ISO 16 standard) | 69.3 Hz |
| A4 = 442 Hz (many European orchestras) | 69.61 Hz |
| A4 = 443 Hz (Berlin, Vienna) | 69.77 Hz |
| A4 = 435 Hz (French diapason normal, 1859) | 68.51 Hz |
| A4 = 432 Hz (alternative tuning) | 68.04 Hz |
| A4 = 415 Hz (Baroque pitch) | 65.36 Hz |
| C4 = 256 Hz (scientific pitch) | 67.81 Hz |
Intervals from C♯2
| Interval | Note | Frequency | Ratio (just) |
|---|---|---|---|
| Minor second | D2 | 73.42 Hz | 16:15 |
| Major second | D♯2 | 77.78 Hz | 9:8 |
| Minor third | E2 | 82.41 Hz | 6:5 |
| Major third | F2 | 87.31 Hz | 5:4 |
| Perfect fourth | F♯2 | 92.5 Hz | 4:3 |
| Tritone | G2 | 98 Hz | 45:32 |
| Perfect fifth | G♯2 | 103.83 Hz | 3:2 |
| Minor sixth | A2 | 110 Hz | 8:5 |
| Major sixth | A♯2 | 116.54 Hz | 5:3 |
| Minor seventh | B2 | 123.47 Hz | 9:5 |
| Major seventh | C3 | 130.81 Hz | 15:8 |
| Octave | C♯3 | 138.59 Hz | 2:1 |
Instruments and voices that can play C♯2
Frequently asked questions
What is the frequency of C♯2?
C♯2 is 69.3 Hz when A4 = 440 Hz (68.04 Hz if A4 = 432 Hz).
What MIDI number is C♯2?
C♯2 is MIDI note number 37.
Is C♯2 on a piano?
Yes – it is key 17 of 88.