Ok Ben ( It seems in recording that you are forever the teacher AND the student...,so you can't drop out on yourself.)
You are PRETTY close (And in part are very much right!)
SOME mixers have BUILT IN EFFECTS (Such as reverb and who knows what else?) So in SOME cases you COULD 'PROCESS' the signal on it's way down it's path or hall or tunnel (Sort of) yes, BUT USUALLY (NOT ALWAYS) what would happen is that you would employ 'OUTBOARD GEAR' which means other units (Outside of the mixer) that do various tasks to the signals (Usually each unit does one thing really well, like a good reverb unit will pretty much just do no nonsense kick ass reverb. SOME very good units do a few things.)
Ok (Remember I mentioned mixers doing other "Side features?"), well the way effects USUALLY fit into the picture is by means of one of these Side Features called "THE EFFECTS SEND & RETURN" This is pretty simple really... See, when the signal comes into the mixer (Like the frontdoor) it can sort of be walking towards the "Back Door" (The Direct Out) , BUT you can kind of tell it to step out of a "SIDE DOOR" The side door is another way Out of the mixer (House) AND a way back In.
So you can tell the signal to go out the side door BEFORE it gets to the back door (Direct Out).
So what happens to the signal when it goes out the side door?
The side door is called the "EFFECTS SEND" AND the "EFFECTS RETURN." There are USUALLY two Jacks (Sometimes more) on a Mixer that we can think of the sidedoor
The Effects Send Jack and the Effects Return Jack.
Now for a little recap.. The signal has come into the Mixer (House) through the Input (Frontdoor) and is headed for the DIRECT OUT (BACKDOOR) but you tell it to hold off of going out the backdoor and instead send it out the Effects Send (side door).
What happens is you hook up a cable (Or cables) to the Effects Send so the signal travels out of the Mixer, down the cable and into A EFFECTS UNIT ( A PIECE OF OUTBOARD GEAR: A seperate box that effects the signals sound.. it could be a Reverb unit the siganal passes through making it sound "Echoy" )
Now you decide "Enough of this effecting, you get in here and get out that back door and damnit look at you...You're all Echoy and sounding like a huge canyon!"
Well the signal needs a way to Return from the effects unit and get back into the Mixer (House) through the side door it went out of...Now how is that gonna happen??
Well ANOTHER CABLE hooks up that the signal travels down back into the Mixer FROM THE EFFECTS UNIT.
What do you suppose the Jack that that cable hooks up to is called??? Lets see, it's has to do with Effects AND it IS Returning into the sidedoor back into the mixer.... AH HA! It must be the EFFECTS RETURN!!!!!
YES! The side door is no damn side door! It's simply TWO JACKS (One leading out of the mixer called) EFFECTS SEND (And one leading back into the mixer called) EFFECTS RETURN!!
So can see that the signal has gone out the Effects Send (Because you are sending it to the seperate unit (For example a Reverb unit) and then the signal is Returning to the Mixer into the Effects Return?
This is the Send and Return (SOMETIMES the Return is called "Recieve".. You may also see the term "Effects Loop" which is another way to call the going out and coming back in of the signal through the Send and Return.
(Now dig this!... Ok, signals are USUALLY recorded to the multitrack "DRY" (With no effects) (An exception MIGHT BE Compression.... SOMETIMES you send the signal to a compressor and then to the recorder.) The reason you'd USUALLY want the signals "Dry" is that you don't want to be stuck with an effected sound on the recording. (Because what if it sounded cool at first, but then you realize you played a master piece guitar solo, but now it sounds it like junk because of all the effects on it? AND they are recorded! So you'll have to do it over to get rid of them!... Screw that!) SO, the way around that nightmare is to use the Effects send and Return at mixdown!!
So when all the recorded sounds are coming back into the mixer you can THEN tell one to go out the side door, tehn when it returns it goes (with all the other signals) to the CD recorder or cassette deck (or whatever) and is recorded there with the effect on it.
SO it looks like you have everything right in your post BUT
I don't understand what you mean by the Mastering Effects Processors (Unless you mean Effects processors used at mixdown like I just described OR there are some digital mastering processors I'm unaware of.)
When I mentioned Mastering I meant it as in terms of how (SOMETIMES) people mix everything to a STEREO TWO TRACK and THEN USUALLY (OR SOMETIMES) another guy sends the Left singal and the right signal through a mixer and it goes through various tasks of FINAL EQ and COMPRESSING AND LEVEL SETTING... THEN it goes to a recorder that makes the CD you buy at the store.
(Mastering really isn't something to even worry about yet at all)
As far as how that 2424 works...I have no idea. (Sorry)
Do searches on Effects units and tell me a few kinds AND do a search on this bbs about INSERTS and what they do for next time.
Be cool