“Let’s say I recorded a live band on ADAT without compressing/limiting because I’m not real sure of myself yet using a compressor and I don’t want to mess with the original signal, or maybe I just don’t have enough compressors to control all the instrument signals simultaneously during a live performance.
“Later, when I want to mix down, maybe some of my tracks are too dynamic or maybe some of my levels weren’t hot enough and others are occasionally too hot and clipping the ADAT meters.
“So, one at a time, I route each track through a compressor and back to another track of the ADAT, to experiment with evening out the dynamics or bringing low levels up and others down. I’m thinking this should make mixing easier because I won’t have to ‘ride’ the faders, and hopefully the final mix will be ‘even’ better.
“But how is the quality of the original signal affected when I route it out of the ADAT and back to another track again, even if I don’t insert any processing between them? Or maybe instead of using a compressor between the original and new track, I decide to control the new signal level with the console faders.
“Is this an acceptable or common practice in ‘real’ studios, or am I way off?”
There are several issues to consider here. First, if your original recording clipped on the way into the ADAT there isn’t much you can do to fix it. You are best served to record at low enough levels to not clip, or even take a chance at clipping the original recording. Of course this is a good reason why compressors are so often employed for capturing live performances.
Routing signals out of your ADAT and back in requires that they go through an additional A/D and D/A conversion, plus be subjected to the cabling and any analog electronics they must encounter along the way. Even if you patch a cable directly between one ADAT output and another input there are issues with the analog electronics in those areas (as is true with any system, not just the ADAT). You can try this for yourself and decide whether there is too much of a compromise in sound quality. Most people wouldn’t do it on a regular basis.
As for the merit of cleaning up and compressing tracks prior to mixing, well, this is probably a personal preference issue. If you don’t have any way to automate your mixdown process a little judicious use of the techniques you mention may be warranted. It depends on how many hands you can get (and need to get) around the mixer to do a good mix. Just remember, the more you ‘do’ to the signal the more at risk it is.
While your setup may work okay now, you probably will realize better results by either adding the processing you really need to your system so you don’t have to rerecord the signals multiple times, adding automation to your mixer (or just get an automated mixer), or adding a DAW to your system. You can transfer your ADAT tracks into it and process and manipulate your tracks at will. Then you can return them to the ADAT for mixing or just mix everything in the computer. Your Sweetwater Sales Engineer will be happy to discuss the pros and cons of each of these solutions with you.