24 Bit Workflow - Double Dither (24, then 16?)

[edit machine]

I'm working in 24 bit in pro tools HD, all ITB. It's been suggested to me that when I bounce back into my sessions (RTD) after going through a plugin mastering chain, that I should be applying 24 bit dither. The way it was explained to me is that the plugins used (waves, DMG Equality, Speakerphone, etc...) and Pro Tools itself have floating point internal resolutions that need to be dithered back down to 24 bit at the very end of the mixing / mastering process. Is this correct?

Then my second question (assuming that I do need this 24 bit internal RTD dither) is how to then deal with the double dithering that would be needed when converting files to 16 bit bit for CD duplication?

Is the first 24 bit dither needed? If so, does this present a problem when re-dithering to 16 bit files?

[mikevarela]

not sure but I know that PT uses a 48bit internal engine and if you stay in the box no dither should be applied. Only on the export and then only do you apply a shape you prefer, often using a mastering limiter like the L2. Noise shaping comes into question, 3 profiles are available. basically they shape the dither out of the area we hear the best (middle).

Try not to dither till the end