The double bass is tuned in fourths: E A D G, the same notes as a bass guitar. Its low E is around 41 Hz, which most phone microphones barely pick up: Tunelight reads the note from the whole sound, so it still finds the right one.
Double bass tuning
| Tuning | Strings | Frequencies (Hz, A4 = 440) |
|---|---|---|
| Standard | E1 A1 D2 G2 | 41.20 · 55.00 · 73.42 · 98.00 |