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Definition: sound card

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 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.

Anatomy of a Sound Card
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.)

High-End Sound Card
This Audigy card from the Creative Labs Sound Blaster family cables to an external hub that supports surround sound with seven speakers and a subwoofer. It provides a wealth of connections for A/V equipment, including ports for MIDI synthesizers and musical instruments.