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PC Hardware in a Nutshell, Second Edition by Barbara Fritchman Thompson, Robert Bruce Thompson

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Sound Card Components

The key function of a sound card is playback—accepting a digital data stream or MIDI instructions from the PC and converting them to an analog audio signal that can be reproduced on speakers or headphones. Most sound cards can also do the converse—accept an analog audio signal and convert it to a digital data stream that can be stored on a PC. Sound cards use the following components to support these functions:

Converters

Sound cards contain at least one Digital-to-Analog Converter (DAC) and one Analog-to-Digital Converter (ADC) for each of the two stereo channels, and some contain more. A DAC converts a digital audio stream into the analog audio delivered to the Line-out port. An ADC digitizes analog sound received from the Line-in or Microphone port. CD-Audio sound, generally the highest quality supported by sound cards, requires 16-bit resolution. The converters used in better-quality sound cards usually support higher resolution, typically 18- or 20-bit. Resolution sometimes differs between the DAC and ADC. For example, a card might use an 18-bit DAC and a 20-bit ADC. Internal resolution is often higher than that supported by the DAC/ADC, typically 24- or 32-bit.

Sample rate generator

The sample rate generator provides the clock for the converters under the control of the PC. While nothing prevents using arbitrary or continuously variable sample rates, most sample rate generators instead support discrete sample rates, which are usually even fractions ...

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