A few questions about creating Impulse Responses

[househoppin09]

I've got some old Multi-FX units lying around and would like to record some IRs for them. I know the basics of how to do it, but am a bit unclear on what the limitations are for what can be done successfully with IRs. Given that I'll be using them with the RV7000MkII, and since some of the best IR discussions I've ever seen have been here on ReasonTalk, this seems like the place to ask!

In no particular order:

- Which FX on a Multi-FX unit can be captured via IR and which can't? I know that the general rule of thumb is "it has to be linear", so presumably reverbs, delays, EQs, tremolos should always be doable, and overdrives, distortions, saturations, enhancers, exciters should never be doable. Do I have that right?

- Which of the above categories would choruses, flangers, and phasers come under? Can those kinds of effects ever be captured with IRs, and what would the limitations be?

- Can IRs properly preserve the stereo or panning aspects of things like stereo delays? Anything to watch out for there?

- Most importantly, some of the FX units I want to sample are quite cheap and therefore have high noise floors and also tend to distort the audio that passes through them to some degree. How will this affect the IR capturing process and can it interfere with the results in any unexpected ways? I'm guessing that when I use the resulting IRs, the original FX unit's background noise as well as any distortion it imposes on the signal will be completely absent, right? But even if they are, I still wonder whether their presence during the sampling process could cause problems or inaccuracies of some kind. This is something I really want to get cleared up.

As you all can see, I'm clearly not that well versed on this! Many thanks to anyone who can help.

[househoppin09]

Any ideas? No need to go painstakingly through all of my questions, I'd be happy enough to get even just one or two of them answered. I know you're out there, IR experts!

[esselfortium]

Choruses, flangers, phasers, and tremolo effects aren't possible to recreate in an impulse response because they rely on modulation over time in such a way that each sample of the input signal is not processed identically to the next. (Having a really difficult time explaining this coherently, hopefully it made sense...)

[househoppin09]

Perfectly coherent, good to have that cleared up. Thanks!