An amplitude window discriminator is described which permits selection of spikes from a multi-unit recording, provided the signal-to-noise ratio is high enough. The device can be built at relatively low cost and time. The circuitry permits analysis of the positive or the negative deflections of the recorded signals. In Part One of the circuitry, the signals are pre-amplified and may be inverted in polarity. In Part Two, the pulses are compared to a variable lower threshold voltage, and low amplitude noise is eliminated. Part Three depicts a logic circuit for elimination of disturbing high-amplitude signals, whose output delivers digital pulses, each corresponding to an original signal (e.g. a neuronal spike) of a certain amplitude.