adding a gain reduction meter to a compressor

I apologize if this has been covered before, ive searched for a couple of days now (here, google etc) and i cant seem to find an answer. Im trying to hook up a GR meter to a ROSS compression pedal, i understand how they work on inputs and outputs, i have the vu meters and i have the driver boards, but how do you hook them up for gain reduction? not just for the ross pedal but in general

thanks guys this was making me nuts! 

This is by no means an easy thing to do and the methods for achieving an accurate idea of how gain is being reduced are very dependant on the gain element as well as the detection system.
It could be FET, VCA, optical, chopper......
Generally you have to find the feed to the gain element and see if you can take a sniff off it to give you something meaningful to send to a display. This isn't always possible. I've seen some circuits (Joe Meek comp for example) where they've used a comparator to compare the original signal to the limited one to show the difference on a meter
I've no idea what the Ross uses in their circuit.
I have used a simple schmitt trigger in the past to give a single LED indication of when gain is being reduced. This was for an optical compressor circuit from a Lexicon - something I've been thinking of doing here as a project. But you have to do a fair bit of work to determine the values - it's not just a matter of finding a test point and sending it to a meter.
Good luck !

The best way to do it is to add another gain element, a duplicate of the one used in the compressor, and run a reference voltage through it. Then use the sidechain to run both gain elements and you should get a pretty close approximation to what is happening in the compressor. This is how the La2A, 1176 etc do it.

Yes that's true for FET limiters (1176) or optical cell types (LA2, 3, 4)
I believe that the Ross compressor referred to uses a CA3080 transconductance amp as a VCA.
Generally with VCA's you can use the control voltage to give an indication of the gain reduction - depending on whether you can interpret the CV as something meaningful for a meter or LED.
Not straightforward !
Interestingly on Urei's BL-40 Limiter - which is a combination of LA3 type and 1176 type circuits, they have taken a feed off the CV to the limiter FET and tweaked it for use on a meter. I believe they do something similar on the 1178.

on a opto compressor with a vactrol can i pull a signal off the led side of the vactrol and feed it into a meter driver for gain reduction? the brighter the leds the more reduction i figure...