I really, really love this mic...(Modded CV4)

There is definitely an issue with phase (relationships) when using any EQ, whether hardware during tracking or mixing, or plug-in. Especially if you are using a radical amount of EQ or EQing more than once. Phase shifting during the EQing process naturally causes phase issues. As for compression, not so much if at all unless you are grouping two or more sources that are gettng group compression that may have phase issues.

Now with regards to compression during tracking, don't be afraid! One should never over-compress at any stage of recording because you can't "un-compress" or decompress later. What goes to tape/disk is your permanent original source recording. That being said, good compression techniques will improve your source recording and make it a whole lot easier to continue tracking and mix later. This is especially true when compression is part of the sound.

For example, when tracking lead vocals it is not only safe but smart to use some opto and FET compression after the preamp going into the converter. The most common Opto compression used is the LA2a or CL1b units or similar (ADL1000, ADL1500, Summit 100 and 200 and the various LA2a clones) where the smoothing effect of the compressor adds a thickness to the tone that cannot really be recreated by another technique. It especially can't be recreated with equalization. It isn't a pumping of bass or lower mid frequencies. It is an alignment of the various frequencies in the program material that creates a thickening effect to the source material. The most common FET compression used is that of a UA 1176 or similar. The FET 1176 family of limiters and clones is primarily used to catch the peaks and prevent overloading into the DAW or tape deck. This can allow you to track with greater confidence.

Which comes first? Two schools of thought. Most say 1176 first to catch the peaks then the LA2a/CL1b to smooth out the entire program material. Then the rest of use like to use the Opto first to smooth out everything and just leave the FET to catch the really big peaks left behind by the slower reacting Opto. FETs are VERY quick...Optos are notoriously slow.

How much do I use? from 1 to 3 db shaved off with each of the Opto and the FET is the most conservative and thus "safer" way of tracking and you still get the thickening effect. If you know what it's supposed to sound like in the final, then you will be more confident with using a greater amount of compression.

Methodology:
In most cases, these days, I am running the preamp out at nominal gain (meaning, the average program material sits around -18DBfs and peaks at around -9DBfs) and then into the LA2a where I usually set the peak reduction at around 5.5 to 6 where it shaves off anywhere from 1 to 12 db on the louder passages. Then make-up gain is tricky because it's also going to feed into the FET 1176 and too much output gain will overload (distort) the 1176. Sometimes this is the sound you want but not often...unless you're tracking really hard rock and metal music forms. So then you are going into a trickier to operate FET where attack and release controls, ratio choice, input and output all have interactive effects on the amount of compression and its behavior will affect your output. You need to strive here to use it to only hit the big peaks. If your output on your Opto is set fairly low, say at 3 to 4, you can get the input of the FET in the normal operating range of about 4 to 6. If it's a little hotter on the Opto output, you'll need to get it down to 2.5 to 3. Attack should be fast, release not so much but not slow either. Ratio for limiting is usually thought of as 12:1 or 20:1 up to "infinity to 1". It' gonna BANG that needle hard on the big peaks and probably nail at about 16 to 20 db reduction according to the meter. Not always entirely accurate but it sure looks extreme! Now you can back off the control and the attack speed and the ratio and take off a lot less. Start low and work towards using as much as you are comfortable with.

Follow these guidelines and you will end up with a buttery smooth and dynamically well-controlled track each and every time.

Your question was " is there any difference at all between compressing during tracking or compressing on the insert during mixing?
Well yes, there is a little... insomuch as you don't have overload protection if you track without compression and rely on the post work to achieve your results. If you overload the input of your DAW or tape deck, you can't undo distortion... although cutting out some 1khz and 2 khz bells will help substantially to return it to "usable". The extra AD/DA conversion in bringing the program material out of he daw and back into again is really not that much of an issue these days...sound wise or horsepower wise. It's common industry practice now and yields as effective a result as it ever did in the purely analog world using the inserts on a console. However, when it comes to vocals, I really really prefer to get the compression right in the tracking stage and end up with a usable track for all overdubs such as backing vocals.
There is also the "hybrid" approach of just using an FET when tracking and leaving the Opto until mixing using an insert as you have pointed to. Sometimes minimal FET limiting is used during tracking and then further amounts of FET along with the Opto are used during playback, overdubbing and mixing.

I think I've rambled on long enough here. I haven't even touched on techniques outside of lead vocal applications, nor the use of other types of Opt compression for guitars and bass and horns and drums, not to mention using hybrid units on bass and other lower register instruments.

No plug-in will ever fatten up a snare like a Rev-F 1176 on a snare going to DAW/tape. you get "the sound" going in and nothing can screw it up...well, tone deafness and stupidity can screw it up but I really don;t think that's in the realm of possibility for the vast majority of us who ply our trade with pride.

Ward EXCELLENT!! THIS is what this board is for! These kind of posts. Wish I had read a post like this when I first started - would've saved me years of bad recordings...I might start a thread about gain-staging too...

I agree, excellent!  A gain-staging one would be great as well.

John, is it possible to have a "Studio Techniques" type of subforum, reserved only for posts like these?  Maybe with no posting allowed, but with exceptional posts copied there by you with appropriate thread titles?

Or sta-level

look-ahead VCA? no idea, not sure what you're getting at

popmann, forgive us, we know not what we do...