Mains electricity in Europe, Africa, most of Asia and Australia alternates at 50 Hz, and that is the frequency of the hum a ground loop or an unshielded cable adds to audio there, with harmonics at 100, 150 and 200 Hz.
Which note 50 Hz is at other reference pitches
“In tune” depends on what A4 is tuned to, so the same frequency is a slightly different distance from the nearest note in each tuning.
| Reference | Nearest note | That note | 50 Hz is |
|---|---|---|---|
| A4 = 440 Hz · Standard (ISO 16) | G1 | 49.00 Hz | +35.0¢ |
| A4 = 432 Hz · “Verdi” pitch | A♭1 | 50.97 Hz | −33.2¢ |
| A4 = 442 Hz · Orchestral | G1 | 49.22 Hz | +27.1¢ |
| A4 = 415 Hz · Baroque pitch | A♭1 | 48.96 Hz | +36.3¢ |
Octaves of 50 Hz
Doubling a frequency raises it an octave and halving lowers it one, so these all have the same note name and the same offset from it.
Harmonics of 50 Hz
A real instrument playing 50 Hz also sounds whole-number multiples of it. The first eight, and the notes they fall nearest:
| Harmonic | Frequency | Nearest note | Off by |
|---|---|---|---|
| 1 | 50.00 Hz | G1 | +35.0¢ |
| 2 | 100.00 Hz | G2 | +35.0¢ |
| 3 | 150.00 Hz | D3 | +37.0¢ |
| 4 | 200.00 Hz | G3 | +35.0¢ |
| 5 | 250.00 Hz | B3 | +21.3¢ |
| 6 | 300.00 Hz | D4 | +37.0¢ |
| 7 | 350.00 Hz | F4 | +3.8¢ |
| 8 | 400.00 Hz | G4 | +35.0¢ |
Period and wavelength
One cycle of 50 Hz lasts 20.000 milliseconds; in air at 20 °C, where sound travels at about 343 metres a second, one wavelength is 6.86 metres.