These amps take an antenna or cable TV signal and boost its strength. The channels on the coaxial cable (whether digital or analog) are Radio Frequency (RF) signals. The amplifiers simply boost the signal level. These signals may be digital, high definition, ATSC encoded, or they might be standard definition, NTSC encoded channels. The amplifier doesn't know or care. It doesn't look at the individual signals, it just amplifies them all.
The primary purpose of an RF amplifier is to boost the signal to overcome losses down the line due to splitters, taps, and long cable runs. They are not intended to improve a signal that is already too weak.