7. Adding Band-Limited Steps

Using a band-limited step, a square wave of any frequency can be synthesized by adding steps of alternating sign at regular time intervals. Here, two band-limited steps are sampled then added together to form one cycle of a band-limited square wave:

A problem with adding band-limited steps to generate a band-limited square wave is that a step's high side extends infinitely to the right. This is easy enough to handle when generating a low frequency square wave where the ripples of transitions don't overlap, but not otherwise.