1.) A low-pass filter is an EQ filter that affects high frequescies; it lets the low frequencies "pass" without being affected. Used to EQ high frequencies up and down.
2.) A high-pass filter is a low-pass filter in reverse in that it's used to EQ the low frequencies while letting the high frequencies pass inaffected.
3.) A Low-shelf filter will EQ boost lower frequencies but will do this boosting in a certain "shape". Hard to descrobe in words, but let's say you have your low shelf set for +3dB starting at 200Hz and maxing at 100Hz. This means that the amount of EQ boost will start at zero at 200Hz and "ramp up" to a maximum of +3dB at 100Hz, with all frequencies from 100Hz down boosted the maximum of +3dB. Picture an EQ curve thats (reading from right to left, high to low) flat at zero boost/cut all the way down to 200Hz. At that point the EQ boot like will start angling up until it reached a +3dB boost at 100Hz. At that point the EQ slope goes straight horisontal agaan at +3dB all the way down to the lowest freqency. This flat line at +3dB is the "shelf" because it resembles a horizontal shelf haigher than the "floor" at zero.
4.) A High-shelf filter is just like a low-shelf, except in reverse; it sets up an EQ boost "shelf" at the high end of the frequency spectrum.
5.) A low-cut filter is just like a low'shelf filter, but it performs an EQ cut instead of an EQ boost; the "shelf' is below zero.
6.) Just like #5, but for the high end of the spectrum instead of the low end.
7.) A limiter is similar to a compressor, but it's stricter. With a limiter you set a maximum peak level above which nothing can peak. If you set a limiter for -3dBFS, that means that nothing will be lounder than -3dB. A -2dB peak will be "limited" to -2dB and not let any higher than that. This is sometimes called "brick wall limiting".
A compressor, on the other hand, throws a "governor" or "dampener" on the peak levels, but does not set an absolute "brick wall" above which nothing can travel like a limiter does. Compressors are set based upon "ain reduction ratios", expressed as something like 3:1 (three-to-one) or 4:1 (four-to-one.) What this means is that if you have your compressor set to, say, 3:1, this means that for every 3dB of increase in a peak going into the compressor, only 1dB of increase comes out. A 6db rise going in will only be a 2dB rise coming out (still a 3 to 1 ratio.) There are other settings like threshold and attack speed, but those are for another discussion. DO a search on "compressor" on this board and you'll find threads that go though it all in detail.
HTH,
G.
