I am new to DSP, I'm trying to implement a low pass filter in a microcontroller and I'm looking for examples on the internet.
One of the simplest low pass filter (as its title says) is this. But I don't understand how is this a low pass filter? All that I see is just an equation
y = 2x - 1
I made a simple example on google sheets and it gave me the same triangle signal with just higher amplitude. What am I missing?