A genuine dulcimer can be tuned in 2 ways: Ionian DAA or Mixolydian DAD. This means that in Ionian mode, the thick string is D (Re), the middle string is A (La), and the thin strings are also A (La) but one octave higher. In Mixolydian mode, it goes like this: The thick string is D (Re), the middle string is A (La), and the thin strings are D (Re) one octave higher.
