[old_tv_nut]

IF refers to the intermediate frequency amplifier stages.

The usual sharpening in the video amplifier section creates a following opposite polarity pulse, that is, to the right of the edge being sharpened; so, a black object gets a white outline on the right side, called an "overshoot." If a circuit can affect the phase as well as the amplitude of the frequency response, like the IF amplifier can, it can produce a leading white transient before a black object, called a preshoot. The typical sharpness control adjusted the frequency response in the video amplifier and therefore changed only the overshoot intensity. Set designers made the IF to produce a fixed desired preshoot to match the middle setting of the customer sharpness control overshoot. It's was a matter of taste to decide what this "middle" amount of sharpness is, and it was baked into the design. Some very late models of analog TVs (like the last Zeniths) had integrated analog video circuits that could control the amount of both preshoot and overshoot simultaneously, which was much more like a studio monitor.