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About A♯0
A♯0 / B♭0 has a frequency of 29.14 Hz in standard tuning, where A4 is fixed at 440 Hz. It is MIDI note 22 and key number 2 on an 88-key piano.
In equal temperament every semitone multiplies the frequency by the twelfth root of two (≈1.05946), so A♯0 is 47 semitones below A4: f = 440 × 2^((22 − 69) / 12) = 29.14 Hz. The number in the name is the octave in scientific pitch notation, which starts each octave on C.
A♯0 and B♭0 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.
A♯0 frequency in different tunings
| Tuning reference | A♯0 frequency |
|---|---|
| A4 = 440 Hz (ISO 16 standard) | 29.14 Hz |
| A4 = 442 Hz (many European orchestras) | 29.27 Hz |
| A4 = 443 Hz (Berlin, Vienna) | 29.33 Hz |
| A4 = 435 Hz (French diapason normal, 1859) | 28.8 Hz |
| A4 = 432 Hz (alternative tuning) | 28.61 Hz |
| A4 = 415 Hz (Baroque pitch) | 27.48 Hz |
| C4 = 256 Hz (scientific pitch) | 28.51 Hz |
Intervals from A♯0
| Interval | Note | Frequency | Ratio (just) |
|---|---|---|---|
| Minor second | B0 | 30.87 Hz | 16:15 |
| Major second | C1 | 32.7 Hz | 9:8 |
| Minor third | C♯1 | 34.65 Hz | 6:5 |
| Major third | D1 | 36.71 Hz | 5:4 |
| Perfect fourth | D♯1 | 38.89 Hz | 4:3 |
| Tritone | E1 | 41.2 Hz | 45:32 |
| Perfect fifth | F1 | 43.65 Hz | 3:2 |
| Minor sixth | F♯1 | 46.25 Hz | 8:5 |
| Major sixth | G1 | 49 Hz | 5:3 |
| Minor seventh | G♯1 | 51.91 Hz | 9:5 |
| Major seventh | A1 | 55 Hz | 15:8 |
| Octave | A♯1 | 58.27 Hz | 2:1 |
Instruments and voices that can play A♯0
Frequently asked questions
What is the frequency of A♯0?
A♯0 is 29.14 Hz when A4 = 440 Hz (28.61 Hz if A4 = 432 Hz).
What MIDI number is A♯0?
A♯0 is MIDI note number 22.
Is A♯0 on a piano?
Yes – it is key 2 of 88.