Adding moving speed control to a circle

Hey guys,
It’s my first time here and i hope you can help me.
It’s kind of difficult to explain, but i’ll try my best!

My project:
I want to create a small white circle, which is moving in front of a black background in the x and y axis. The circle is drawing a line (feedback loop works fine).

I control the circle with a midi input, so one knob of my midi controller is for the x position of the circle, the other one for the y.
Now i want to add a speeding up feature, with which i can control the speed of the circle. I want to achieve a nice and smooth motion.

My idea is to map (for example) the knob of the midi-controller for the x-axis to the “center x” path of the circle. Now when i move the knob to the left (from -1 to 0), i want to add a litte bit of speed to the left direction. When move it to the right (from 0 to 1) i want to add speed to the right direction. When the knob is in the center position (0) the circle shouldnt move in any direction.

Does somebody know a class or something for this?

Sorry for my bad english and explanation, i’ll hope you know, what i mean.

Best regards,