Fliss,something I forgot to mention,WHAT I described as a fiddle roll,is a long roll,fiddlers also use short rolls eg a [d note]
could be played with four notes ,e D c sharp D.I find the best way of thinking of them is single grace notes before the main note.and as i said beforefor a short roll ,you can do the cuts with your index finger as an ALTERNATIVE eg eDeD or eDaD.