Sound Blaster X-Fi in the context of Sound card

In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as from fingers touching a touchscreen, sound entering a microphone, or light entering a digital camera, into a digital signal.

An ADC may also provide an isolated measurement such as an electronic device that converts an analog input voltage or current to a digital number representing the magnitude of the voltage or current. Typically the digital output is a two's complement binary number that is proportional to the input, but there are other possibilities.