High-Low Pass Slider?

Hi, I’m searching to see if there’s a plugin that lets me apply a High/Low pass filter in the same way as the Sliding Time/Pitch Shift. As in, something that slowly applies a pass filter to an audio track instead of it suddenly changing. If it helps, I’m trying to create an audio of someone going into a cave, and the outside rainfall is slowly muffled, however I can’t make the transition between the unaltered and pass filtered audio as seamless as I like.

Does anyone know of a plugin that would let me do this?

One simple way is to duplicate the track, apply a low-pass filter to the duplicate, then crossfade from one to the other.
I don’t have any rain recordings handy, so this little demo just uses noise:

FilterFade.ny … https://forum.audacityteam.org/t/high-low-pass-slider-filter/45315/4

Thank you! This works perfectly!