Handy private archive of dbx reference material and service manuals...
The manual for the 224X which is different in that it adds front panel lightshow and level adjustments. Otherwise, functionally the same.
Be advised that this is a two-ended system that must be used on Playback if it is used on Record. Don't bother using it for anything but analog TAPE. CDR-Audio has plenty of dynamic range and no noise floor to speak of.
If you dont already have one, I advise you to get a dbx 400x or 400x-ds to manage the 224 and any other processors you may have. It is an amazing piece of equipment that allows you to place 3 processor loops before or after the encode/decode loop, or bypass them altogether or in any combination, PLUS you can dub encoded or non-encoded music to or from either encoded or non-encoded music unlike the previous dbx 200 or 200x. I have the 224x plus a 400x and a number of other dbx, Pioneer, BSR, Carver, BBE, SAE and ADC goodies; and have created some impressive cassettes back in the day, given the limitations in speed stability. Now-a-days I make impressive CD's of old analog source recordings with improved dynamics, less noise and zero wow and flutter.
Look for a 400x on eBay. Snipe it at the last 10 seconds if you don't want to bid against yourself..