The zynaddsubfx intro runs you through setting up basic square waves. The parameter for the pulse wave oscillator changes something like the duty cycle. (See Nullsleep for more info.) Pulse wave voices with different duty cycle are easy to differentiate when pulse wave voices with the same duty cycle might not be; in "Deep Sparse" I used two different duty cycles to differentiate the BGM from the main voice.

Blue Sky design by Jonas John.