(TGC) Time gain compensation is the signal processing control that allows the sonographer to amplify the returning signal from deeper structures in the body. The TGC control compensates for the attenuation of sound waves.

(ADC) A system that receives analog input data and produces digital values at its output. Analog to digital converters are used by the ultrasound scanner to convert the received signal into a format more compatible with the computer systems.
Ultrasound front-end-systems as well as many others sophisticated electronic systems use these analog signal processing components in connection with e.g., low-noise amplifier (LNA), and time gain compensation amplifier (TGC) as key elements in determining the overall system performance.

See also Digital to Analog Converter, and Digitization.

Reject is a time gain compensation control that allows the sonographer to reduce the returning signal from more shallow structures in the body.