This paper describes the design of a bilinear time-frequency distribution which is a joint model of temporal and spectral masking. The distribution is used to generate temporally evolving excitation patterns of nonstationary signals and systems and is conceived as a tool for acousticians and engineers for perceptual time-frequency analysis. Distribution time and frequency resolutions are controlled by a separable kernel consisting of a set of low-pass time and frequency smoothing windows. These windows are designed by adapting existing psychoacoustic models of auditory resolution, rather than using mathematical window functions. Cross-term interference and windowing clutter are highly suppressed for the distribution, ensuring resolution accuracy over a dynamic range sufficient to encompass that of the auditory system (in excess of 100 dB). Application to the analysis of a synthetic and two real signals are included to demonstrate the approach.