This amplitude discriminator is designed for audio and sub-audio signals such as extracellular nerve action potentials. For every waveform peak that appears “within” the window aperture set by the user, a pulse is generated at the “Within Window” output. Signals that exceed the upper level of the window produce a pulse at the “Above Window” output. A visual indication of the pulses is provided at each output by the LED display. Both the input signal and the window aperture settings are visible at the multiplex port as shown below in the upper trace. By viewing the input signal as well as the “window” discriminator levels at the multiplex port provides a convenient visualization and ease in setting up an experiment.

Model 121’s multiplex circuitry samples input signals and window levels on a 70%/30% basis respectively, minimizing loss of signal information. The Lower Level control sets the lower discrimination level, and the Window Aperture control sets the upper window level with respect to the lower level setting. This means that changing the lower level setting has no effect on the window aperture except to displace the window up or down. It is impossible to set the lower level higher than the upper level, a feature unique to Model 121. The pulses from either output (Within Window or Above Window) are generated by the falling edge of the analyzed signal as it crosses the preset levels. Because the logic circuit is not time dependent, Model 121 can be used to analyze signals of any duration. Ten-turn controls with dial indicators allow precise setting and direct reading of the window levels. Enclosure includes a tilt stand for bench operation. Rack mounting hardware is optional.