From here: https://www.superbestaudiofriends.o...easurements-and-review.915/page-4#post-262702 All distortion is bad. However, I'd gather that a distortion pattern where successive harmonics are lower than the one just prior is typical or ideal. SET amps have this distortion pattern. People always like to talk about tube distortion. But the BIG one is that dynamic driver transducers (including compression drivers) also have this distortion pattern. And transducers' distortion a magnitude or two (or three) higher than that of amps an DACs. Hence I would posit that a 3rd harmonic higher or even than the 2nd harmonic is not typical or normal. This is why so many IEM nerfs such as @shotgunshane, @Kunlun, or myself long for the next Sony EX1000 which uses a DD, or why @Hands find the well-regarded CFA Andromeda a mess, or why @OJneg prefers the Jupiter and remarks on its glorious mids (which for a BA driver, actually has even 2nd and 3rd order distortion in that region) Even GRAS doesn't get it right in the highs as it produces coupler induced peaks which vary in amplitude and frequency based on insertion depth. This is why I urged @crinacle to stay with this cheapo DIY rig for the high measurements on the IEMs.