This article is from the CD-Recordable FAQ, by Andy McFadden (email@example.com) with numerous contributions by others.
VariRec ("Variable Recording") is a Plextor feature intended to let users
modify the laser power when recording audio CDs. It only works for audio
CDs recorded at 4x. The theory is that adjusting the laser power up or down
slightly may result in better-sounding discs for a particular combination
of writer and media.
VariRec II increases the write speed to 8x and allows manual selection of
the "write strategy" as well.
In theory there is no need for such a feature, because drives contain tables
of power levels for known brands of media, and can automatically determine
the correct setting for others. However, some discs use the wrong media
type information, so manual adjustments can be helpful in some cases.
See section (4-18-2) for information about audio CD quality, and (3-31)
for some notes on recording speeds and power levels.