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What are the possible kinds of nonlinearity in a system?

Mar 27, 2019
I often see harmonic distortion and IMD in the freq. domain, and deviation from linearity in amplitude. Is there a corollary or some theorem in signals and systems suggesting that these three exhaust all forms of nonlinearity?

In another thread it was suggested that amplifiers might have distortions that we do not measure. I guess IMD is not thoroughly explored, only two or three frequencies are usually measured. Also, deviation from linearity is not explicitly reported with amplifiers, only the clipping point gets mentioned (I know that amps are assumed to be operating within their linear range).

My understanding is that most other reported specs would be manifest in imperfections in HD, IMD, or amplitude problems. For instance, Slew rate is supposed to show as harmonic distortion. Could there be anomalous behavior with no footprint in what we measure from frequency and amplitude responses?


Major Contributor
Jul 21, 2018
The Neverlands
Distortion basically is a deviation from the input signal.
This can be caused by numorous things.
It can be characterised in the amplitude, frequency, phase/time domain.

All the types of distortion will result in deviations in one or more of these areas.
They are all electrical and can be measured.
Certain aspects can be displayed in various ways and certain types of distortion can be isolated from others.

Some forms are more benign than others. Also audibilty thresholds differ per type of distortion (and individual). Audibilty thresholds of test tones do not necesarilly also apply to music. In general one can easier detect test tone distortion than distortion in music as the brain has other things to do when interpreting music than when it just has to discern one or 2 tones.

HERE is some easy to read/comprehend basics on it that does not use formulas that few fully comprehend.
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