# linear and non linear distortion

#### Ghina Bayyat

Joined Mar 11, 2018
135
i have a question
what is the difference between linear and non linear distortion in amplifiers ? and how could it be that there is a LINEAR distortion ? and what about phase and amplitude and frequency or harmonic distortion are they linear or non linear ??

#### BR-549

Joined Sep 22, 2013
4,928
It will matter how you define distortion. If we put a wave form in.........and get a wave form out, with some change in shape.......it would be non-linear distortion.

In my humble opinion.......if the amplitude only is changed.........I would call that linear distortion. I think flat gain is linear distortion.

But I'm weird. And that might not help you on a test or interview.

#### recklessrog

Joined May 23, 2013
985
If this is in the context of an exam, I think an example of Linear distortion could be frequency response changes in the output signal compared to the original.
If say the input signal was flat from 10 Hz to 20 kHz, and due to for example tone controls the output had some frequencies boosted or cut, then you could say there is Linear distortion.
Maybe others here may have a different opinion though.

#### BR-549

Joined Sep 22, 2013
4,928
I figure distortion is change. And if the change is constant to every part or instant of the signal.....it's a linear change/distortion. A non-constant change.......it's non-linear.

I really don't know.....just seeing what can be dug up. I never really thought about it. There ought to be an official definition somewhere.

There will be some audio experts on here later.......they work with this stuff. I was always surprised at the level of distortion a circuit can take and still function.

#### recklessrog

Joined May 23, 2013
985
Now I am questioning my own answer, If the tone controls in my example were only acting on part of the frequency spectrum, then that could be Non Linear distortion. If however, the output amplitude rose or fell in a linear fashion, say for instance, 3 db per octave, then that is a Linear change, and as BR-549 says, change is distortion.

#### Ghina Bayyat

Joined Mar 11, 2018
135
so by defining distortion as the change in the signal i can say that amplitude distortion is a linear distortion because it is a change but it is a desired change because the amplifier has to amplify the signal and it changes linearly with the input signal
and the frequency distortion is a non linear distortion because the harmonics are a fraction of the fundamental frequency and it doesn't change linearly or in a constant amount of change
if what i said is right then what should i consider phase distortion ?linear or non linear ? and can i say that the linear distortion is a desired distortion and the non linear distortion isn't ? is this true ?

#### crutschow

Joined Mar 14, 2008
31,097
Any distortion that changes the frequency content (not the frequency response) such as harmonic and intermodulation distortion, are non-linear.
Changes in frequency response or phase can be considered linear distortion if you want to use that term (I don't).
Yes, generally I would say linear distortion is desired (or not undesired), and non-linear distortion is not desired (at least in audio amps, expect for rock bands ).