In a system for calibrating PAM4 signals, an equalizer determines a first signal amplitude measurement of the PAM4 signal. The equalizer determines a first signal boost measurement of the PAM4 signal. The equalizer determines whether the first signal boost measurement and the signal amplitude measurement are substantially consistent with each other. Responsive to determining that the signal boost and the signal amplitude are not substantially consistent with each other, the equalizer determines a reference amplification modification and calibrates a PAM4 signal according to the determined reference amplification modification.