Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!valid!caber!lou
From: lou@caber.valid.com (Louis K. Scheffer)
Newsgroups: comp.dsp
Subject: Re: Question about distortion
Message-ID: <499@valid.valid.com>
Date: 27 May 91 00:33:27 GMT
References: <1991May23.070428.23505@funet.fi>
Sender: news@valid.com
Lines: 26

varri@cs.tut.fi (V{rri Alpo) writes:

>Harmonic distortion is nonlinear distortion characterized by the
>appearance in the output of harmonics other than the fundamental
>component when the input wave is sinusoidal.

>What is the name of the distortion which does not appear at the
>harmonic frequencies of the fundamental component but at some
>other frequencies? This type of distortion is often introduced
>by nonlinear filters.

In RF work these are called "spurs", which is short for spurious
responses (or outputs).  You often find them at f+60Hz, f-60Hz,
f+-(twice the IF frequency), etc.  Sometimes they are considered
part of the "noise", even though they are correlated with the input.
In audio work you get "intermodulation distortion", where some
non-linearity produces sum and difference frequencies from two pure
tone inputs.  In digital work you get "aliasing".  For example, a
3 KHz square wave into a 44.1 KHz sampled system (say CDs) might
produce an 0.9 KHz output if the input filter was not good enough.
(From the 15th harmonic of the input aliased by the 44.1 KHz sampling
rate.)  I'm sure there are additional technical names, but most people who
work with them call them things that shouldn't be repeated around
small children.

-Lou Scheffer