If Filter Blend is set to the top position, you only hear the effect of Filter 1.
If Filter Blend is set to its lowest position, you only hear the effect of Filter 2.
In between these positions, the filters are crossfaded. You hear the effect of both filters.
You can also crossfade the filters when they are cabled in series. In this situation, the distortion—controlled by the Drive parameter—also needs to be considered, as this can be positioned either before or in between the filters, depending on the Filter Blend setting you choose.
In Logic Pro, set up a modulation routing as follows: modulation target FltBlend, source LFO2.
Adjust the settings of LFO 2.
Download the guides:
Logic Pro User Guide: PDF