As can be seen in figure 4, the post-masking effect varies with the length of the masker burst, from 5-10 ms up to 200 ms. This effect is exploited in the coder by a one-pole filter on the masking threshold over time:
The final output mask is then taken as . With this definition, a short burst does not affect much, while a longer burst will sustain the masking for a number of frames even though goes low again.