Also called a sound board or audio card, a sound card is an expansion card for the PC that generates sound and provides audio output to external amplification devices, such as speakers or headphones.
Sound cards are necessary for nearly all CD-ROMs and come standard in computers these days. Many motherboards include high definition audio cards built right in, and third party cards are widely available. Many media center enthusiasts get a surround-sound card to enhance their experience.
Onboard sound either uses a Realtek or Crystal chip or is built into a SuperIO chip (aka southbridge) almost all of the time.
Data from the file to the sound card doesn’t degrade until it hits the DAC, where it may. This is one of the areas (also in acceleration and CPU utilization) where good add-on cards excel. There is quite a bit of electronic noise with onboard solutions, and so there is only a certain level of sound quality which can be reach (which has been improving, might I add … onboard sound today is usually very very good).
PCI add-in cards are capable of higher clarity, and for professional solutions there is usually a PCI add-in card for all of the digital doings and the analog audio pathways and DACs are in an external shielded box.
So far I see no EMU10k1 or EMU10k2 chips onboard, so until then we’re still dealing with Via, Crystal, Realtek, Intel and AMD sound solutions.