A sound card (also referred to as an audio card) is a peripheral device that attaches to the ISA or PCI slot on a motherboard to enable the computer to input, process, and deliver sound.

The sound card's four main functions are: as a synthesizer (generating sounds), as a MIDI interface, analog to digital conversion (used, for example, in recording sound from a microphone), and digital to analog conversion (used, for example, to reproduce sound for a speaker). The three methods of sound synthesis are through frequency modulation (FM) technology, wavetable, and physical modeling.

FM synthesis is the least expensive and least effective method. Sounds are simulated by using algorithms to create sine waves that are as close to the sound as possible.

For example, the sound of a guitar can be simulated, although the result does not really sound very much like a guitar. Wavetable uses actual, digitally recorded sound samples stored on the card for the highest performance.

Physical modeling is a new type of synthesizing, in which sounds are simulated through a complex programming procedure. Some sound cards can also have sounds downloaded to them.

Creative Lab's Sound Blaster is the de facto standard sound card, to the extent that some people use the name as a generic term.

Most sound cards in the past have been Sound Blaster-compatible, because most programs that use the sound card have been designed that way. Sound cards were once all connected to the ISA slot.

However, because connection to the PCI busoffers advantages such as improved signal to noise ratio and decreased demand on the CPU, sound cards being produced today are intended for use with a PCI bus.
Some sound cards, such as Diamond MX300 and SoundBlaster Live!, have 3-D capabilities enabled by processors on the card that use mathematical formulas to create greater depth, complexity, and realism of sound.

High quality audio can be produced through a system that uses the Universal Serial Bus (USB) and does not require a sound card. Processing is left to the CPU, and digital-to-audio conversion to the speakers.

http://www.justvb.net/it/