Available for download, PSPAudioWare PSP X-Dither is a plug-in that protects your mixes from truncation noise when you export a 24-bit recording in 16-bit files. If you're in the market for a dither with different selectable noise shapes, this plug-in is definitely worth a gander, as it's been endorsed by famed mastering engineer Bob Katz. Use this plug-in during the mastering process, specifically when you export the final master into a CD-quality 16-bit / 44.1 kHz file.
This plug-in overlays exceedingly low-level, randomized noise under your audio source to mask the rounding errors that occur when downgrading from 24-bit to 16-bit files. Sometimes these rounding errors can be audible, which is where this low-level noise comes in handy, as it blankets those audible errors with a barely-audible veil of noise. This plug-in goes farther by shaping the randomized noise in various, selectable ways, so that you can always push this noise out of the way of important, programmatic material.
PSP X-Dither is compatible with Mac and Windows platforms. It will operate in AU, VST, RTAS, and AAX formats.