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A sound card (also known as an audio card) is a computer expansion card that facilitates the input and output of audio signals
to/from a computer under control of computer programs. Typical uses of sound cards include providing the audio component for
multimedia applications such as music composition, editing video or audio, presentation/education, and entertainment (games).
Many computers have sound capabilities built in, while others require additional expansion cards to provide for audio capability.
Sound cards usually feature a digital-to-analog converter, that converts recorded or generated digital data into an analog
format. The output signal is connected to an amplifier, headphones, or external device using standard interconnects, such
as a TRS connector or an RCA connector. If the number and size of connectors is too large for the space on the backplate the
connectors will be off-board, typically using a breakout box, or an auxiliary backplate. More advanced cards usually include
more than one sound chip to provide for higher data rates and multiple simultaneous functionality, eg between digital sound
production and synthesized sounds (usually for real-time generation of music and sound effects using minimal data and CPU
time).
Digital sound reproduction is usually done with multi-channel DACs, which are capable of multiple digital samples simultaneously
at different pitches and volumes, or optionally applying real-time effects like filtering or distortion. Multi-channel digital
sound playback can also be used for music synthesis when used with a digitized instrument bank, typically a small amount of
ROM or Flash memory containing samples corresponding to MIDI instruments. A contrasting way to synthesize sound on a PC uses
"audio codecs", which rely heavily on software for music synthesis, MIDI compliance, and even multiple-channel emulation.
This approach has become common as manufacturers seek to simplify the design and the cost of sound cards.
Most sound cards have a line in connector for signal from a cassette tape recorder or similar sound source. The sound
card digitizes this signal and stores it (under control of appropriate matching computer software) on the computer's hard
disk for storage, editing, or further processing. Another common external connector is the microphone connector, for use by
a microphone or other low level input device. Input through a microphone jack is often used by speech recognition software
or for Voice over IP applications.
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