But Linda Anderson says there are little flourishes that set it apart, like ringing strings. "Ringing strings is a really common feature. So playing more than one note at the same time. And that was largely in Shetland because there were no other instruments playing for a dance. So it was one fiddler in a corner and a roomful of people dancing. So they had to make as much sound as they could and make that rhythm come out."
This is a common feature in Appalachian fiddle as well. My grandfather was an old-time West Virginia fiddler. I have his fiddle; the fingerboard, nut, and bridge have been filed down to make them flatter, so that it's difficult to play the middle strings without brushing an adjacent string, and playing three strings at once is easy.
In Appalachia in the old days it was often just a fiddler playing for a dance, or one fiddle and one banjo. Both instruments emphasised rhythm- yes there's a melody, but the melody is embedded in a matrix of rhythm and drones.
And yes the fiddles were often tuned AEAE, which gives you plenty of droning possibilities.
Edden Hammons b. 1875 one of the earliest West Virginia fiddlers to be recorded, here as a very old man, out of practice, and on a borrowed fiddle! (He evidently didn't own a fiddle at the time of the recording, they had to go borrow one.)
You can hear the near-continuous droning/double-stops
https://www.youtube.com/watch?v=KHJbZr_zMj0