Generally speaking, steep signal edges are required for the processing of digital signals; however, notably externally supplied signals which are conducted, for example, via long cables are liable to have comparatively flat signal edges. By selecting appropriate switching thresholds, delays between an input signal and an output signal of a circuit can be minimized. The circuit selects the first switching threshold at a low value of the input signal and switches the first threshold value to a second, higher threshold value when the input signal exceeds a further, higher threshold value. Thus, an output signal is generated comparatively quickly after the beginning of the positive-going or negative-going edge of the input signal. This can be realized by switching over the switching threshold of a comparator or by utilizing two comparators. Switching over to the various switching thresholds, or the various comparators, is provided by a further control circuit which may also be driven by the comparators themselves. A particularly high insensitivity to interference is achieved when use is made of two comparators which themselves are constructed as Schmitt triggers.