We have investigated the way in which stimulus variability will affects the attenuation characteristic or auditory filter shape inferred from masking experiments. Stimulus variability was found to have a pronounced effect on filter shapes derived from bandlimiting experiments in which the signal is a tone, the masker is a band of noise centered on the tone, and the independent variable is the width of the noise band. But stimulus variability had virtually no effect on filters obtained from notched noise masking experiments. In an attempt to extend the utility of the filter‐shape concept we have replicated an earlier experiment in which the masker is two tones rather than noise. The tones, each 57 dB SPL, were used to mask a narrow band of noise centered midway between them and threshold for the noise signal was measured as a function of the frequency separation of the tonal maskers. The form of the data is in good agreement with the auditory filter shape derived using a notched‐noise masker and a tonal signal. In order to predict the absolute levels obtained in the noise‐masking experiments, it was necessary to assume that internal noise adds to the variability of the stimuli. The resulting model, which incorporates the filter shape from the notched noise experiment and the energy detection model, predicts not only the form but also the absolute levels obtained in the bandlimiting and notched noise experiments. In addition, it predicts the shape of the data from the two‐tone masking experiment but it does not predict the overall level.