Postmasking stays at simultaneous-masking level for 5ms then decays to quiet by 200ms.

Evidence

A Gaussian-shaped condensation impulse with a duration of only 20 Ils produces a spectral shape that corresponds to that of white noise. It is similar to that of a Dirac impulse. Post masking produced by a white-noise masker can therefore be measured without spectral influences using such a brief Gaussian impulse as a test sound. The peak value of this Gaussian impulse expressed in level is plotted as the ordinate in Fig. 4.22, which shows the level necessary to just reach threshold in post masking as a function of delay time td from the end of the masker. The parameter in the figure is the overall level of the white-noise masker. The solid lines indicate results that show almost no decay for the first 5 ms after the masker is switched off. There, the values correspond to those measured in simultaneous masking. After about 5ms delay time, the threshold in postmasking decreases and, at about 200 ms delay time, reaches the threshold in quiet. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 515

Categorization

• DEFINE: Explains how a brief Gaussian impulse can substitute for white noise as a test sound, isolating temporal from spectral masking.