You can have AD/DA converter, compressor/limiter, mic-pre, power-amp, reverb, delay...etc in rack form. Almost anything that you can think of, can be in rack form.
You can apply compression in all kind of recording situations, do not limit yourself to just drums recording.
I always like to record vocal with a compressor or limiter.....here a picture of my vocal signal chain.
u87 -> manley tnt mic pre -> vari-mu -> ssl converter
for home recording, i would recommend you just use software plugs as mentioned by blueprint. google rack units and you will realize there are a host of different types. perhaps head on down to sospubs.co.uk or tweakheadz for some reading. i find the latter more enjoyable.
[QUOTE= Guitar>amp>mic>preamp>mixer>pc via protools/audition/etc
but what are the rack effects for?
the compressors and EQs.
what other rack effects are there?
I usually go for the first line of amplification, which is the microphone (that is if u are not using DI & stuff). I prefer the 'big' sound, so i use a reasonable $$ big diaphragm mic for tis purpose. Next is pre-amp, a good mic-pre can extend the depth & width of yr sound, which equals to big sound. When u have all these, yr sound efx comes in, whether rack or plugs-in or pedals etc.... Effects are good to have if use properly.
Experiment & get yr own sound. I use to record my gtrist with one mic front & one mic behind on a peavey gtr amp, and one ambience mic inside my HDB toilet, and w all three tracks, we can mixer, colour, efx, etc.... yr ears will tell u wat is good! Good luck!
Basically, audio processors are segregated into two types (1) Dynamic Processors; and (2) Effects Processors.
Dynamic Processors are devices that alters the...well, dynamics of a sound (check what dynamic of a sound means if you are interested); slight changes to the envelope characteristics. These include Compressors, Limiters, Gate, aural exciter, stereo widener, EQ, etc. These are usually used to adjust give loudness (perceptively), presence to a sound; prudent and passive measures to prevent clipping of a track; to remove unwanted/unhealthy frequency bands or adding missing bands.
Effect Processors are devices that alters the behaviour of ADSR, which in turn changes the timbre of a sound. These include your reverberations, delay/echo, filters, chorus, flanger, modulation, vocoder, distortion, ring modulation, tremelo, wah-wah, etc... there are dedicated single serving effect racks unit (analog or digital) like filtering racks (sherman filterbank II), vermona ring mod I, and there are multi-purpose all in one effects racks.