Ab0 — 25.957 Hz
Ab0 (A-flat 0) is 25.957 Hz in standard equal temperament at A=440 Hz. It is MIDI note number 20.
Ab0 Frequency in All Tuning Systems
| Temperament | Frequency (Hz) | Cents from Equal | Common Usage |
|---|---|---|---|
| Equal Temperament | 25.957 Hz | 0.00 | Modern standard; piano, fretted instruments |
| Pythagorean | 26.104 Hz | +9.78 | Medieval/early music; string ensemble open fifths |
| Just Intonation (Major) | 26.163 Hz | +13.69 | A cappella vocal, barbershop, Renaissance |
| Just Intonation (Minor) | 26.163 Hz | +13.69 | Minor-key vocal music, string ensembles |
| Quarter-Comma Meantone | 25.701 Hz | -17.16 | Renaissance keyboard, early Baroque organ |
| Third-Comma Meantone | 25.617 Hz | -22.83 | Renaissance vocal music in minor keys |
| Sixth-Comma Meantone | 25.783 Hz | -11.64 | Baroque orchestral ensemble compromise |
| Werckmeister III | 26.015 Hz | +3.86 | Baroque keyboard; Bach contemporaries |
| Werckmeister IV | 25.927 Hz | -2.00 | Baroque keyboard, strong key contrast |
| Werckmeister V | 25.927 Hz | -2.00 | Specialized Baroque keyboard |
| Kirnberger III | 26.015 Hz | +3.86 | Classical-era keyboard, keys near C major |
| Vallotti | 26.015 Hz | +3.86 | Baroque/Classical orchestral tuning |
| Young (1799) | 25.986 Hz | +1.93 | Classical-era keyboard |
| Bach/Lehman | 26.015 Hz | +3.86 | Bach keyboard works, Well-Tempered Clavier |
| Neidhardt | 25.986 Hz | +1.93 | 18th century keyboard, near-equal alternative |
| Kellner (Bach) | 26.015 Hz | +3.86 | Bach keyboard reconstruction |
Positive cents = sharper than equal temperament. Negative cents = flatter. 100 cents = 1 semitone.
Ab0 at Different Concert Pitches
The same note varies in frequency depending on the concert pitch standard used by your ensemble.
| Concert Pitch | Frequency (Hz) | Common Usage |
|---|---|---|
| A = 440 Hz (ISO standard) | 25.957 Hz | US, UK, and most modern ensembles worldwide |
| A = 442 Hz | 26.075 Hz | Many European orchestras; France, Germany |
| A = 443 Hz | 26.134 Hz | Berlin Philharmonic; some US orchestras |
| A = 432 Hz | 25.485 Hz | Alternative tuning; Baroque revival |
| A = 415 Hz (Baroque) | 24.482 Hz | Historically-informed Baroque performance |
f = f_at_A440 × (concert_pitch / 440)
Ab0 and G#0 — Enharmonic Equivalents
Ab0 and G#0 are enharmonic equivalents — they sound identical at 25.957 Hz but are written differently depending on the musical context.
Ab0: A♭ appears as the tonic of A♭ major and is common in flat key signatures. Common key signatures: A♭ major, D♭ major, E♭ major.
G#0: G♯ appears in sharp key signatures and is the leading tone in A major. Common key signatures: A major, E major, B major, F♯ major, C♯ major.
Enharmonic equivalents share the same frequency in equal temperament. In historical temperaments like Pythagorean or meantone, they may differ slightly.
Why Ab0 Varies Across Tuning Systems
Ab0 shows a maximum deviation of -22.83 cents in Third-Comma Meantone compared to equal temperament. This 23-cent difference is clearly audible to trained musicians and reflects how different tuning philosophies prioritize interval purity over equal distribution.
In Third-Comma Meantone, Ab0 is tuned flatter than equal temperament, reflecting this system's approach to distributing the Pythagorean comma across the chromatic scale.
5 of the 15 non-equal temperaments deviate by more than 10 cents for Ab0, making this note one where tuning system choice has a meaningful impact on pitch.
Ab0 Across All Tuning Systems
Explore how Ab0 is tuned in each historical temperament system. Each tuning system gives Ab0 a slightly different frequency, affecting the harmonic character of chords and melodies.
Tune Ab0 with precision — Get Tunable.
Tunable supports 15+ tuning systems including equal temperament, Pythagorean, just intonation, and historical well-temperaments. See exact Hz values in real-time as you play.