Which control determines the amount of amplification occurring in the receiver?

Overall gain controls the amplification of all the received ultrasound signals uniformly. This adjustment affects the brightness of the entire image by increasing or decreasing the amplification of the echoes returning from all depths. It is a primary control for adjusting image brightness. The overall gain should be set to an appropriate level to ensure that the ultrasound image is neither too bright (over-gained) nor too dark (under-gained), allowing for optimal visualization of the anatomical structures.

American Registry for Diagnostic Medical Sonography (ARDMS). Sonography Principles and Instrumentation (SPI) Examination Review Guide.