In reference to vacuum tubes, what is "tube rolling"?

"Tube rolling" is the very simple (but potentially expensive...) hobby, of regularly swapping the vacuum tubes in your amplifier, CD player or whatever, to see how different tubes affect the sound. In theory, you will eventually find a set of valves (tubes) that give you the sound you like.

It means trying several different tubes in each socket

and deciding which one produces the most preferable sound character.

Technically, any tube that is good

should sound the same as any other good one,

but some people just will not believe it

no matter what you tell them.

Never heard the term before.

I'm wondering if you may mean tube saturation, or perhaps the process of biasing the tube to operate within the linear range of the tubes output.