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About A♯4
A♯4 / B♭4 has a frequency of 466.16 Hz in standard tuning, where A4 is fixed at 440 Hz. It is MIDI note 70 and key number 50 on an 88-key piano.
In equal temperament every semitone multiplies the frequency by the twelfth root of two (≈1.05946), so A♯4 is 1 semitone above A4: f = 440 × 2^((70 − 69) / 12) = 466.16 Hz. The number in the name is the octave in scientific pitch notation, which starts each octave on C.
A♯4 and B♭4 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♯4 frequency in different tunings
| Tuning reference | A♯4 frequency |
|---|---|
| A4 = 440 Hz (ISO 16 standard) | 466.16 Hz |
| A4 = 442 Hz (many European orchestras) | 468.28 Hz |
| A4 = 443 Hz (Berlin, Vienna) | 469.34 Hz |
| A4 = 435 Hz (French diapason normal, 1859) | 460.87 Hz |
| A4 = 432 Hz (alternative tuning) | 457.69 Hz |
| A4 = 415 Hz (Baroque pitch) | 439.68 Hz |
| C4 = 256 Hz (scientific pitch) | 456.14 Hz |
Where to play A♯4 on a guitar
Standard tuning (E A D G B E), frets 0–22.
- 4th string (D), fret 20
- 3rd string (G), fret 15
- 2nd string (B), fret 11
- 1st string (high E), fret 6
Intervals from A♯4
| Interval | Note | Frequency | Ratio (just) |
|---|---|---|---|
| Minor second | B4 | 493.88 Hz | 16:15 |
| Major second | C5 | 523.25 Hz | 9:8 |
| Minor third | C♯5 | 554.37 Hz | 6:5 |
| Major third | D5 | 587.33 Hz | 5:4 |
| Perfect fourth | D♯5 | 622.25 Hz | 4:3 |
| Tritone | E5 | 659.26 Hz | 45:32 |
| Perfect fifth | F5 | 698.46 Hz | 3:2 |
| Minor sixth | F♯5 | 739.99 Hz | 8:5 |
| Major sixth | G5 | 783.99 Hz | 5:3 |
| Minor seventh | G♯5 | 830.61 Hz | 9:5 |
| Major seventh | A5 | 880 Hz | 15:8 |
| Octave | A♯5 | 932.33 Hz | 2:1 |
Instruments and voices that can play A♯4
- Piano (88 keys)
- Guitar (standard tuning)
- Violin
- Viola
- Cello
- Harp
- Flute
- Clarinet (B♭, sounding)
- Oboe
- Bassoon
- Alto saxophone (sounding)
- Tenor saxophone (sounding)
- Trumpet (B♭, sounding)
- French horn (sounding)
- Trombone
- Tenor voice
- Alto voice
- Mezzo-soprano voice
- Soprano voice
Frequently asked questions
What is the frequency of A♯4?
A♯4 is 466.16 Hz when A4 = 440 Hz (457.69 Hz if A4 = 432 Hz).
What MIDI number is A♯4?
A♯4 is MIDI note number 70.
Is A♯4 on a piano?
Yes – it is key 50 of 88.
Where is A♯4 on the guitar?
In standard tuning: 4th string (D), fret 20; 3rd string (G), fret 15; 2nd string (B), fret 11; 1st string (high E), fret 6.