automatic cutoff while playing notes?

[spin]

hi all guys

i am not an espert so i need your help...I don't know how to make an envelope on the cutoff that works alone while i am playing the keyboard. What i would like to do is a low pass filter that closes and opens periodacally in automatic while playing some notes (without turn left and right the cutoff knob i mean). What type of settings i have to do on filter cutoff amp etc??

thanks for any help