Abstract: Test equipment for measuring the amplitude of certain a.c. signals and comprising, a signal processing means responsive to each of such a.c. signals for transforming that signal into a d.c. level signal of a magnitude proportional to the r.m.s. amplitude of the a.c. signal, an analog to digital converter responsive only to those of such d.c. signals having magnitudes within an acceptance range for the converter to provide binary indications representative of such magnitudes of those signals, and circuit means for causing only d.c. level signals derived from a.c. signals with r.m.s. amplitudes in a subrange of a full range of such amplitudes to fall within the acceptance range of the converter.