Direct boxes, A/D converters?

[Xipe]

What the hell are they?
Why would I want one?
For what would I want one? My guitar (direct-recording), for vocals... or?

Trying to learn the ropes here.

[AlChuck]

A direct box takes a low-level signal like that from guitar or bass pickups, etc. and brings it up to line level so that it can be plugged into mixing boards, tape ins, sound card ins, and anything else that wants a line level signal.

An A/D converter takes a line level signal and digitizes it -- turns it into digital codes that represent the voltage of the signal at a very brief instant of time -- 44,100 times per second for so-called CD-quality audio. 16 bits are used to encode the voltage values at each of these instants at CD quality. The more bits, the more finely resolved the audio. Kind of like in a photo, where the more dots-per-inch used to represent the image, the more clear, smooth, and realistic it is to the perception.