Rolled 8ths means: The first quaver is played twice as long as the second.
Swing and shuffle are example idioms played in rolled 8ths.
Semiquavers, crotchets, minims, triplets and hemiola are not rolled. They are played straight. Only quavers roll.
Not every melody is suited to rolled 8ths.
Swing is an idiom always played with rolled 8ths.
What makes swing? Cross rhythm. Often drums and electric bass will be the only instruments supporting the beat. All other sections will be playing cross rhythms.
Anticipated notes are integral to swing. There are always plenty of tied notes in swing.
Our 8ths feel ballad returns (sped up) to show us what shuffle is all about.
A shuffle beat is a fast ballad beat with rolled 8ths.
Now we know what shuffle is, we need to know how to write for it.
Don't write shuffle as above. Above looks too much like a ballad beat. Drummers don't get the feel right if you write shuffle like that.
Remember, 8ths are rolled. So is this what shuffle looks like? Try giving this to a drummer. He'll throw it at you!
This is the way to write shuffle.
Write rolled 8ths as dotted quaver semiquaver. This is the way to write shuffle for the player to get the feel right. 8ths are still played rolled, with the first quaver played twice as long as the second.
Here is the above swing piece written shuffle.
You might be given a piece like this with no indication of it being shuffle. If it sounds ugly and contorted played straight, shuffle it. If it rolls well, roll it.
NB You never see two beamed quavers in shuffle notation; they are always written dotted quaver semiquaver.