Also called a "sound board" or "audio adapter," it is a plug-in card that records and plays back sound. Supporting both digital audio and MIDI, sound cards provide an input port for a microphone or other sound source and output ports to speakers and amplifiers. Sound circuits are typically built into the chipset on the motherboard, but can be disabled if a separate sound card is installed. See Sound Blaster, AC'97 and HD Audio.
Digital Audio
Digital audio files contain soundwaves converted into digital form. Sound cards convert the digital samples back into analog waves for the speakers using digital signal processing (DSP). See sampling, digital audio and DSP.
MIDI
MIDI files contain a coded representation of the notes of musical instruments such as middle C on the piano. Taking considerably less space than digital audio, MIDI files require a wavetable synthesizer on the card, which holds digitized samples of the instruments. See MIDI.
PC sound cards typically have all the components in this picture. Some have only one output, which may be amplified (Amp) or not (Buffer amp). These components may also be built directly into the motherboard. (Illustration courtesy of Peter Hermsen.)
This Audigy 4 Pro sound card from Creative Labs' Sound Blaster family cables to a remote-controlled external hub that supports all major surround sound standards, up to seven speakers and a subwoofer. It provides a wealth of analog and digital inputs and outputs for connecting audio and video equipment and even has ports for MIDI synthesizers and musical instruments.
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