1.6.4 Threshold Range Scale factors can be defined on a sliding scale around the threshold value. See parameterTHRESHOLD_RANGE. When the THRESHOLD_RANGE option is not used (default), the scale factor is equal to 1 (not filtered) when the amplitude is below the threshold value and equal to the value specified by the parameterATTEN_FACTOR when the amplitude is greater than or equal to the threshold. When a threshold range is used and the band amplitude is within the threshold range, the scale factor is computed by a cosine-squared function yielding values between the minimum scale factor and 1.