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In Reply to: RE: By all means posted by Pat D on November 16, 2015 at 12:55:30:
I'm an EE too and he's not speaking my language. His statement makes no sense at face value, because harmonic distortion will result from any non-linearity. It's not the only form of distortion, but it's often the biggest.
Categorically speaking, linear distortion is just the deviation in frequency magnitude and phase response. These are the deviations that can be caused by a linear transfer function.
Categorically speaking, non-linear distortion is every other deviation that correlates with the signal, which distinguishes it from noise and interference which are deviations that are uncorrelated with the signal.
If you stimulate a non-linear system with a single pure sine wave at frequency f, all distortion products will occur at multiples of f. This is harmonic distortion.
If you stimulate a non-linear system with a multiple sine waves at frequencies f1,f2,f3,..., the harmonic distortion products will occur at multiples of f1,f2,f3,... Also, the sine waves will intermodulate at the sum and difference frequencies. That is a mix of harmonic distortion and intermodulation distortion.
You can generalize the above to any signal.
At first I wasn't sure what point he was trying to make by distinguishing harmonic distortion from non-linear distortion. I thought he might be suggesting that THD and/or a plot of the harmonic distortion spectrum is insufficient to characterize amplifier distortion. But nope, he seems to think that the only distortion that matters is clipping (which is harmonic by the way).
I don't know where that leaves IM distortion in its various forms. If Arny is trying to suggest that harmonic distortion is negligible but non-linear distortion is not, that only leaves IM distortion in its various forms. That plays right into the hands of Otala, Jung, Curl, et al who have been pointing out for a long time that high NFB designs with insufficient OLB that minimize THD produce unwanted TIM/SID. But I'm quite sure that's not what Arny thinks.
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Follow Ups
- Harmonic distortion is non-linear distortion - Dave_K 19:58:40 11/16/15 (1)
- RE: Harmonic distortion is non-linear distortion - Pat D 15:02:36 11/18/15 (0)
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