This comes up from time to time so I thought I'd post some data.

http://irc.nrc-cnrc.gc.ca/pubs/fulltext/ir766/ir766.pdf Courtesy of the NRC in Canada

http://www.soundproofingcompany.com/upload/IR-766.gif

Note that there's not much performance gain after R19

I' not smart enought to know what I'm looking at so I'll just ask the stupid question. I have some insulation left over and wondered if putting some scraps in the floor joists over the rec. room will have any effect?

Certainly not a bad question at all. Since it's scrap and there's no possible harm, why not?