USB and FireWire interfaces can be used to connect to external sound cards that are virtually immune to electrical noise from your computer (Figure 3-6). Because they move the digital-to-analog conversion outside of your computer, they are good choices for notebook computers that do not have line-out jacks. External sound cards can also provide more input and output jacks and mixing controls than most internal sound cards. See Chapter 2 for descriptions of several USB and FireWire sound cards that work well for audiophiles, DJs, and musicians.
Figure 3-6. USB audio connection to stereo