I hope I have not confused you (or anyone else) with these explanations. Trying to put the concept into layman's terms is lot trickier than I thought. In technical terms the objective is:

To create 4 independently controllable, low frequency (0.5-8Hz) channels of analog signals (triangle waveform in this case) using digital modulation (such as PWM) with the LED's acting as a low-pass filter.

Now that sounds a lot easier to do, doesn't it?