How Does a Sound Card Work?


A sound card is a circuit board installed in a computer that allows the PC to manipulate sound through speakers and microphones. Each card has software called a driver that communicates with Microsoft Windows, so the card works with apps such as games and media players.

Inputs and Outputs

Sound cards have several 3.5 mm mini jacks accessible to the user; you connect speakers, headphones and other audio equipment to these jacks. Basic cards have jacks for line-level input, microphone input and headphone output. More sophisticated cards have additional jacks for more speakers and additional audio sources. Sound card jacks have a standard color code that indicates what function each jack performs. For example, the lime green jack provides a line-level output suitable for headphones or powered speakers, and the light blue jack is a line-level input.


Sound card installation typically happens in two steps. The first step is the physical installation of the sound card itself, in which you open the computer, locate the motherboard, and insert the sound card into an empty Peripheral Component Interconnect slot. The second step is the installation of the card’s driver software, which is downloaded from an install CD or from the manufacturer’s website. Many modern PCs and notebook computers come with a basic sound card already built in, including the driver software. Unless you’re building a computer from scratch or need enhanced audio capabilities, you don’t need to add a sound card to your PC.

Sound Playback

When you play a movie on your computer, for example, the media player program sends audio data from the movie soundtrack to Microsoft Windows, which in turn passes the data to the sound card’s driver software. The driver takes in the data, stores it in the sound card, and issues a command to the card to play the sound. Electronic circuits in the card convert the data into audio signals, which headphones or speakers turn into sound.

Sound Recording

A line level audio signal from a microphone preamp, musical keyboard or other device enters the sound card through the line level input jack. The electronic circuits in the card convert the audio signals into a stream of computer data. A program, such as the Sound Recorder accessory in Windows, receives the data from the card’s driver program. The recording program processes the data and saves it as a file on the computer’s hard drive, where it may be played back at a later time.

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