Well, alrighty then. I'm not very good at this stuff, but I'll try and give you just a few. Here's some specs on the Mackie VLZ Pro mixer:
* Ultra-wide 0-60dB gain range
This basically tells you how much gain it has. What it
doesn't tell you is that the more of it you use, the crappier it sounds.
* 130dB dynamic range for 24-bit, 192kHz sampling rate inputs
This is basically some extra marketing gobbledy-gook. Ignore it.
*+22dBu line input handling
This is pretty important, as it has to do with the amount of headroom you've got to work with. This also happens to be a pretty impressive figure for a cheap mixer, by the way. In simple terms, it means you can use it louder sources (drums), or higher-output mics with less fear of distortion.
Distortion under 0.0007% (20Hz-20kHz)
I'm not exactly sure how this is measured, but again, in layman's terms it has to do with how clean your signal will be -- pretty obvious, right? Anyway, this is a pretty good figure, too, for a cheap mixer. Take it with a grain of salt -- it's a good thing to look at when comparing the transparency of some of the pres out there.
But it doesn't take in to account the
type of distortion that 0.0007% is composed of.
If it's the yucky kind, then be relieved that it's only 0.0007%, but if it were the good kind, then you may want even more of it, as is the case with quality tube gear. Chances are you won't find much of the good kind with inexpensive stuff.
Two more things you should look at if they're published:
slew rate - this is a measure of how accurately it will respond to transients. It's a speed measurement. Higher and/or lower slew rates are what makes a mic pre "fast" or "slow."
The difference? Fast is usually associated with greater accuracy and detail, while slow is often associated with terms like "warm," and "vintage," etc. This is a realm that is almost completely a matter of personal taste, so keep in mind that faster isn't necessarily better.
Impedence/loading -- A preamp's input impedence is a fairly complex subject that would require at least a page or two of explanation. To simplify, it's a measurement (in ohms) of how the preamp's input is going to react with the microphone's output. Same principle behind speakers and receivers. Just be wary that mics will have a certain impedence that they want to see at a pre's input, and that loading is something to be wary of, as it will often have an effect on the sound.
In general, this is something you will have to consider a lot more when dealing with lower-output dynamic mics, condensers with transformer outputs, and especially ribbon mics. Most transformerless condensers you won't have to worry about as much, as they are much less sensitive to loading.
This is another potentially deceptive figure, as it doesn't take in to account the type and/or quality of input stage. Transforemer inputs, for example, will often deal with loading mismatches quite well . . . but that also depends a lot on the quality of the transformer.
So many things to consider, here. What I've found to be a general rule, though is that higher impedence usually means more detail / less bass, and lower impedence means better handling of sibilances, not as harsh-sounding, etc. This is very generally speaking, though.
My first anwer / explanation is much more relevant than anything I've mentioned in this post.
