Any other waveform than Sinus produces harmonics. To figure out, how they sound, I have written a Pulse-Quad-Morpher, which morphs a Pulsewave with different pulse width (middle slider) into a quadric curve waveform (top slider). The bottom slider is to adjust the frequency. Note, that zero and one are illegal values for the pulse width, since only one value is produced, which is not a waveform.