Question about Filters in AKAI Software 1.9

Hi Guys

I have this question for a long time.
So... Im in Program Edit trying to put my Low 4 (i.e.) filter.
Right under the Cutoff and Reso knobs there are 4 other parameters called Modulation Sources and they stand for:
V>Start V>Attack V>Envy V>Filter

Can anyone please explain to me what are these knobs for in technical terms ?

Thanks in advance