I notice differences on the CD's when I A/B after different treatments.
I was most surprised by the difference between CD's after I did a test in freezing discs. First I would place some blank CD-R's in my freezer for 48-72 hours (it was suggested that doing this would be the equivalent of about 80% of what cryo does). Then I would take the original CD and record to a blank unfrozen disc. Next I would record the original unfrozen disc to a formerly frozen CD-R. Lastly I would put the original CD in the freezer for 48-72 hours and after removing them I'd would record to a frozen disc.
After all that I could tell the difference in quality between all the CD-R's, frozen & unfrozen, even on a car CD player. Go figure. Now I always place new CD-R's and DVD-R's in the freezer for a few days before recording on them.