General Characteristics
Most sound cards use a digital-to-analog converter (DAC), which 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 phone 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, an auxiliary backplate, or a panel mounted at the front. More advanced cards usually include more than one sound chip to support higher data rates and multiple simultaneous functionality, for example digital production of 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 multichannel DACs, which are capable of simultaneous digital samples at different pitches and volumes, and application of real-time effects such as filtering or deliberate distortion. Multichannel digital sound playback can also be used for music synthesis, when used with a compliance, and even multiple-channel emulation. This approach has become common as manufacturers seek simpler and lower-cost sound cards.
Most sound cards have a line in connector for an input signal from a cassette tape or other sound source that has higher voltage levels than a microphone. The sound card digitizes this signal. The DMAC transfers the samples to the main memory, from where a recording software may write it to the hard disk for storage, editing, or further processing. Another common external connector is the microphone connector, for signals from a microphone or other low-level input device. Input through a microphone jack can be used, for example, by speech recognition or voice over IP applications.
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