first of all, realize this is not a linear display. you are seeing harmonics of 120hz that would be nearly invisible on an oscilloscope. it looks as if many of these harmonics are at least 60db less than the signal you are looking at, which is much smaller than the 1% or so resolution of an oscilloscope. there is an oscope display in SpectrumLab. the good thing about SL is that you can use the specialized functions of higher end sound hardware, including the higher sampling rates (192khz last time i looked) if your card has that capability. the other interesting feature of SL, that takes some playing with to begin to understand, is the "virtual audio lab" with oscillators filters, modulators, etc.. that make it extremely versatile.