Right, so there you are late at night--what about just putting the guitar right into the mixing board? After all, the plugs look like they're the same. Besides, it's late and don't want to mike your guitar amp. Okay, go right ahead, plug right into the board and you would probably get something that sounds like this.
guitar right into board (8 bit 200k)
Not so good, eh? It sounds sort of "flat". Not at all like a miked amp. So what went wrong?
Well, impedance for one thing. I don't want to get too technical here but suffice to say that the guitar pick-up is a very high impedance and the most mixing boards (if not all) are expecting a much lower impedance signal. You have an impedance mismatch. The upshot of all this is that your guitar signal loses a lot in mid to high frequency range and ends-up sound a bit life-less.
So if we could find a way to match the impedances it might sound better--and a common way to do this is with a direct box or DI. Now a D.I. can be passive or active but both do the same thing--they take a high (or very high) impedance signal and convert it into a low impedance signal that is matched better for your mixing board mic-pre amp.
Here's what the guitar sounds like going through a D.I. and*then* into the mixing board.
guitar via D.I. (8 bit 200k)
Quite a bit better, right? In fact, sort of a cool if your looking for a super clean sound. (By-the-way, this is a popular way to record electric bass.) But for guitar it's not the most convincing rock sound. It's a little too bright for one thing. When a guitar goes through a guitar amp the speaker(s) acts as a low-pass E.Q. Why? Because there's no woofer/tweeter combination only the full range speaker. As a result, the high end gets rolled off and the mid-range gets pumped up. Also, the amp's electronics play a big part in the sound of the guitar. Most good guitar amps use tubes (as in vacuum tubes) instead of transistors.
So, to get *that* sound you ether need to mike an amp (and in my opinion, that's the way to go--if you have the time) or use one of the popular amp emulator boxes. These boxes try to do what all that amp/fullrange speaker combo does. Some try with tubes and some without. The box I used doesn't use tubes at all but sounds fairly convincing.
guitar through black box (8 bit 200k)
Now here's all three examples one after another.
(right into mixer, using D.I. and little black box) (8 bit 600k) or (16 bit 1200k)
So you *can* record electric guitar without using an amp... But don't get lazy--IMHO, if you can, miking a guitar amp is the way to go.