The Minimum dB command lets you set the minimum dB (decibels) which will be shown by ScopeFIR. This is useful primarily on Frequency Response plots. The frequency responses of most FIR filters tend to have very low attenuation in at least some portions of the stopband--for example, maybe 200 dB or more. Generally, attenuation is not of great interest beyond a certain level. Therefore, this option lets you clip the minimum dB so that these very large attenuations don't consume the vertical (Y) resolution of the Frequency Response plots. Note that this is a global setting: ScopeFIR will not produce any decibel value less than this value in any display. The default minimum dB is -130, which is adequate for most applications.  It shows maximum attenuations of 130 dB. For filters in which you are trying to achieve large attenuations, you may wish to increase this to a larger (negative) value such as -150 or -200 dB to see the filter response without clipping in the stopband. If you change this setting, be sure to enter a negative value.