"That's likely a setting that is off somewhere is my guess. Some kind of digital noise created in the audacity file (I'd guess it's something between the sc and audacity perhaps a sampling rate mismatch)?"
when i analyze the spectrum in audacity, the harmonics are not there, just a runup to the 50hz spike, then a rather rapid rolloff afterward.
"The abrupt start and stop of your signal creates frequencies other than 50Hz. The strongest is at 5Hz because the total signal lasts .2 sec. Those extra tones modulate the 50Hz tone and create the sidebands above and below 50. Note the approx 5Hz spacing of the sidebands."
when i extend the length to .4 seconds (20 cycles), i get more ripples, not less.
then, i run a 15 second sample from audacity, and get this.
you can see the weirdness is on the start and stop. over most of the range the tone at 50hz looks as i would expect. however, the harmonics are still present.
when i plot the spectrum in audacity, the 15 second sample looks the same as the 5 and 10 cycle samples (no harmonics).
"I don't have any experience with Spectrum Lab so I don't know why it's creating those odd order distortion products centered at 150, 250, etc. Maybe it's clipping? Try generating a signal with lower amplitude and see if those go away."
i can see the waveform in audacity, so i know it is not clipping there.
then, i turned the volume down by 50%, and get this:
apparently the harmonics were being generated in spectrum lab because of clipping. now, that seems like a problem because who knows how much content was the result of spectrum lab clipping (in all the spectrum lab plots)?
the reason i was interested in this is because some time ago ricci posted some spectrum lab plots of drum hits and they had that same spreadout looking frequency response, which didn't make sense to me because the fundamental of a drum should not be spread over 15-20hz or so, it should be pretty tight. drum shots are around 5-6 cycles or so, btw.