A digital sound card is a computer part most commonly used to translate electronic signals into audio signals that can be played through speakers. A sound card is designed in one of two ways, either as a separate part that plugs directly into a computer's motherboard, or built-in as part of the motherboard itself. A card also has various input and output jacks into which things such as speakers and even musical instruments can be plugged. Modern sound cards are capable of advanced audio functions, such as surround sound, and some can provide sound on a level comparable to dedicated home theater systems.
The two main purposes of a digital sound card are digital playback and music synthesis. Digital playback is simply the output of prerecorded music, whereas music synthesis is on-the-fly generation of sounds as a result of user input. A good example of this kind of technology is the use of a musical instrument digital interface (MIDI) keyboard plugged into a sound card. As keys on the keyboard are pressed, the sound card can generate notes based on stored data files of different kinds of instruments.
Sound cards were not standard equipment in computers until around the 1990s, before which time the most common sounds emitted from the typical computer were basic bleeps and bloops through a single internal speaker. Gradually, and driven largely by the computer game industry, digital sound technology progressed to include more complex audio. Increasingly, things such as sound effects, musical scores and even digitized voice acting became possible through hardware processing by a digital sound card.
Basic digital sound card technology in the early 1990s provided only one-channel mono output, as opposed to stereo or five-channel surround. In addition, the number of different sounds that could be played at once, a characteristic known as polyphony, was limited to no more than three. As a result, for a number of years the sounds that could be played by a computer were no more complex than a ring tone on a basic cell phone. Notably, early sound cards also typically included game ports, the only way for users to plug joysticks or controllers into their computers.
Increasingly through the 1990s, sound card technology improved, and more advanced features such as stereo output became standard. In addition, more cards came to have their own random access memory (RAM) and central processing units (CPUs). This meant that the processing of audio could be offloaded from the computer's main memory and CPU, freeing up system resources for other tasks and allowing a user to maximize sound quality at the same time.
Beginning around the turn of the 20th century, an increasingly common practice for computer manufacturers was to incorporate basic sound cards into a computer's motherboard. This integrated solution is cheaper and takes up less physical space in a computer's case than one that needed to be plugged in to a slot. Features of on-board sound cards are generally minimal, however, and serious gamers and other power users still consider an add-on digital sound card essential.