At A4 = 440 Hz the erhu’s inner string is D4 = 293.66 Hz and the outer string is A4 = 440 Hz. A tuner hides the arithmetic, but knowing it helps. You can match a reference to a recording or a group, judge how far off a string is by ear, and decide whether the peg or the fine tuner should move.
01 The two target frequencies
Standard erhu tuning is inner D4 and outer A4, a perfect fifth apart. In equal temperament, the tuning every chromatic tuner uses, D4 sits seven semitones below A4, so D4 = A4 × 2−7/12, about A4 × 0.6674. At A4 = 440 Hz that makes D4 = 293.66 Hz. Change the reference and both targets move by the same number of cents, so the fifth between them never changes.
02 Both strings for every A4 reference from 428 to 452 Hz
| A4 reference | Inner D4 (Hz) | Outer A4 (Hz) | Cents from 440 |
|---|---|---|---|
| 428 Hz | 285.66 | 428.00 | -47.9 |
| 430 Hz | 286.99 | 430.00 | -39.8 |
| 432 Hz | 288.33 | 432.00 | -31.8 |
| 435 Hz | 290.33 | 435.00 | -19.8 |
| 438 Hz | 292.33 | 438.00 | -7.9 |
| 440 Hz | 293.66 | 440.00 | 0 |
| 441 Hz | 294.33 | 441.00 | +3.9 |
| 442 Hz | 295.00 | 442.00 | +7.9 |
| 443 Hz | 295.67 | 443.00 | +11.8 |
| 444 Hz | 296.33 | 444.00 | +15.7 |
| 445 Hz | 297.00 | 445.00 | +19.6 |
| 446 Hz | 297.67 | 446.00 | +23.4 |
| 448 Hz | 299.00 | 448.00 | +31.2 |
| 450 Hz | 300.34 | 450.00 | +38.9 |
| 452 Hz | 301.67 | 452.00 | +46.6 |
A cent is a hundredth of a semitone. It is the same size on every string, which is why tuners read in cents and not hertz. One hertz is a bigger step on the D string than on the A string: near A4 it is about 3.9 cents, near D4 about 5.9 cents. Moving the reference from 440 to 442 Hz raises both targets by 7.9 cents; moving it to 432 Hz lowers both by 31.8 cents, almost a third of a semitone.
03 Peg or fine tuner
Use the peg for large changes and the fine tuner, if your erhu has one, for small ones. A fine tuner has a short range, and once its screw runs out it can’t move the string any further. So get close with the peg first, then finish with the fine tuner. Tune the outer A first, then the inner D, then check A again, because moving one string can pull the other slightly.
04 Approach the pitch from below
Finish every adjustment by raising the pitch. If a string is sharp, lower it a little below the target and bring it back up. Ending with an upward turn leaves the peg holding against the string’s pull, which is the direction it has to hold. Turn in small movements and bow the string between turns; a big turn on a thin string can overshoot by more than a semitone.
05 Hear it: beats
Two notes that are close but not equal make a slow wobble called beating, and the number of beats per second is their difference in hertz. Play a reference A at 440 Hz and bow an open A that is really at 437 Hz, and you hear about 3 beats a second: the string is about 12 cents flat. As you tune closer the wobble slows, and when it stops the string matches the reference.
If you tune the fifth by ear instead of with a tuner, you may settle on a pure 3:2 fifth. With A at 440 Hz that puts D at 293.33 Hz, about 2 cents below the equal-tempered 293.66 Hz. Both are reasonable; just know which one you chose, especially if you play with a keyboard or backing track, which use equal temperament.
Related reading
Questions
What frequency is the erhu D string?
293.66 Hz when A4 = 440 Hz. It is D4, seven semitones (a perfect fifth) below the outer A4 string.
What is the erhu tuned to at A4 = 442 Hz?
The outer A4 string is 442 Hz and the inner D4 string is 295.00 Hz, both 7.9 cents above the 440 Hz targets.
Should I use the peg or the fine tuner?
The peg for large changes, the fine tuner for the last few cents. Soloist Erhu's tuner suggests the fine tuner within 30 cents of the target and the peg beyond that.
Why tune up to the note instead of down?
Ending with an upward turn leaves the peg holding against the string's pull, which is the direction it has to hold. If you overshoot, go below the note and come back up.