Discrimination experiments were performed for changes in the amplitude of two-tone complexes. Thresholds were measured, among other things, as a function of bandwidth and center frequency. Usually, the overall intensity was roved in each and every presentation to prevent subjects from using loudness cues. The results show that changes in the spectral shape of broadband two-tone complexes can be perceived with and without a roving intensity level. For narrow-band signals, attempts have been made to explain the results in terms of the EWAIF model [Feth, Percept. Psychophys. 15, 375–378 (1974)]. This model could account for the data for signal bandwidths of 1 semitone or less. Modified EWAIF models did not yield better predictions. Thresholds for a change in the spectral shape were measured as a function of sensation level. The ``near-miss'' to Weber's law was not observed. This result is consistent with excitation pattern models.