Use the Effects>Utilities>HDR Compander before an effect has the 32bit warning set to compress range, then you use it after the effect set to expand the range. A more complete explanation in in the Help Documents. Look Here for that info.
the explanation is a little confusing. So if your effects stacking order is: 2 low dynamic range effects followed by a HDR effect and followed by 2 more LDR effects you would have a total of 4 instances of the HDR Compander effect with each pair sandwiching the LDR or would you just have one pair of the HDR Compander sandwiching the whole stack?
Reading the complete explanantion it make me wonder if its a good idea because of the trade off. Do you use this often? or should it be avoided when possible.
I always wrap effects that require compression and expansion with the HDR compander. If your project requires that you insert an 32 bit effect between two lower bit effects then you would have 4 instances as you suggest. There is no trade off. The Compander returns the dynamic range to the pipeline so that the advantages of the higher bit rates are maintained.
If you do not use the HDR compander then everything in the render pipeline after the first instance of an effect has a bit depth warning will only be processed using 8bit color.