Recent research has suggested the existence of a modality-independent memory system that is responsible for storing representations of simple, scalar stimulus attributes, such as the frequency of an auditory pure tone or the duration of a stimulus. In the present study, we modify an existing computational model of short-term memory (STM) for stimulus frequency to allow it to perform STM tasks for both stimulus frequency and stimulus duration, supporting the notion of a common scalar STM system. We further demonstrate the utility of the model by showing that it can reproduce the subjective shortening effect, a classic finding in the psychophysical literature.