The sound they're getting is from the notes and scales they are playing through, not necessarily the instrument... at least, that is what gives it it's most distinct sound.

In a lot of traditional Eastern music, a lot of smaller and more precise intervals are used to give it the distinct sound, hence the difference you hear on the fretless guitar. Quarter steps and even less are much easier to hear.

But more than that, you should look into some "Eastern" scales, as they most definitely do not use the same tonal system that us Westerners are used to. If anything, start yourself off with the harmonic minor scale, get a feel for how it sounds, and expand from there.

Oh and to play either one of those pieces, you're going to need some pretty good chops
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