simulating modulation fx´s with LTspice..AC analysis variable with time?

[dschwartz]

Hi there, i´ve been chewing the idea of designing a phaser (or any other modulation fx).
Since i´m really not a big fan of using the breadboard before simulating a circuit, i´m stuck on thinking how i´ll be able to visualize the changes on frequency response against LPF voltage changing over time.

Maybe i can simulate the LPF output with a DC voltage and make different simulations for different voltages to get an idea of how the filters respond to different input voltages. But i´d like to hear your experience on this, if you have better ideas.

Also, i´d like to use the 4049 variable resistor trick. has anyone simulated that on LTspice?

regards