Sound Card, audio input, line/mic
It takes a physical connection to the computer to make your analog (real world) sound into digital (computer generated) sound. Once a sound is in the computer, it is considered "computer generated". Although there are many different sound cards out there, for the most part, it is the software that makes the difference in performance.
Step 1: What is a Sound Card?
A sound card is a small, usually green, card that is installed inside your computer. The connection to the computer is a small strip of gold electrodes, and the connection to the camera is on the outside edge of the card.
Step 2: Inputs
Most sound cards have an input for line in, mic in. Sound cards are not designed to support video input.
Step 3: Outputs
The only output on a capture card is usually a speaker out option. Sound cards are not designed to support video out.
Step 4: Memory
Sound cards can have memory on them, although, in actuality, the performance difference in normal usage is not measurable.