*Please note that I'm not asking for help in fixing my noise issue. I've already fixed it.  

This question is more about describing the issue and using correct terminology.*

I have two small 5V servos that are powered by a bench supply about 10cm away.

However, the two servo's signals are carried by a two-conductor speaker wire to an arduino **2.5 *meters*** away. (1 "cable" with 2 conductors, each carrying a servo signal, plus 1 extra separate 2.5m wire for common ground.) 

[![speaker wire](https://i.stack.imgur.com/UpgXc.png)](https://i.stack.imgur.com/UpgXc.png)

[![schematic](https://i.stack.imgur.com/rI6cv.png)](https://i.stack.imgur.com/rI6cv.png)

Here is the scope output of the original signals:

[![Servo signal noise with no caps](https://i.stack.imgur.com/1mhRP.png)](https://i.stack.imgur.com/1mhRP.png)

Notice that **`Signal A`** is showing a huge spike on **`Signal B`**'s falling edge.  

The result was that the servos were not independant, and directly affecting eachother. 

Below is the result after placing 0.1μF ceramic caps between each signal and ground, just before the servos themselves:

[![Servo signals with filter caps](https://i.stack.imgur.com/9M7cR.png)](https://i.stack.imgur.com/9M7cR.png)

While **`signal B`** still isn't perfect, the servos no longer appear to affect one another. 

Circuit with caps:  

[![schematic with caps](https://i.stack.imgur.com/71tej.png)](https://i.stack.imgur.com/71tej.png)

---

What would be the biggest likely cause of the original issue, and how do I properly describe how the capacitors solve it? 

I am thinking that the issue was mostly the long distance. However since the signals were affecting eachother, I'm wondering if it could also be related to the two signals being directly next to each other (crosstalk)?

I'm also wondering about how to properly explain the solution using the correct terminology.  

The caps create a low-pass filter, right? But it that also "decoupling"? Because the signals seemed "coupled" before I added the caps. I'm not sure if calling them "decoupling capacitors" is proper