Harmonic Distortion of step-approximation to sine wave

[The Phantom]

Except of course that you naturally generate only a properly dithered
step approximation, in which case there is no harmonic distortion.

The usual definition of harmonic distortion (THD) used in the audio
business is: Total RMS of harmonics alone/Total RMS of wave

There is a website with some good graphics concerning dither and its
effects on harmonics: http://www.cadenzarecording.com/dither.html

Could you explain, perhaps with reference to some of that site's
figures, how dither of a single frequency sine wave can give a result
having no harmonic distortion?

 

[Ben Bradley]

The usual definition of harmonic distortion (THD) used in the audio
business is: Total RMS of harmonics alone/Total RMS of wave

There is a website with some good graphics concerning dither and its
effects on harmonics: http://www.cadenzarecording.com/dither.html

Could you explain, perhaps with reference to some of that site's
figures, how dither of a single frequency sine wave can give a result
having no harmonic distortion?

Very short answer: The signal still has 'distortion', the dither
turns it into random noise, spread out over the whole available
bandwidth instead of being harmonically related to the sine wave.

Here are a couple more good dither links:

http://www.national.com/an/AN/AN-804.pdf

http://digido.com (Click on articles, then dither)

 

[The Phantom]

Very short answer: The signal still has 'distortion', the dither
turns it into random noise, spread out over the whole available
bandwidth instead of being harmonically related to the sine wave.

Here are a couple more good dither links:

http://www.national.com/an/AN/AN-804.pdf

http://digido.com (Click on articles, then dither)

I can see that this question is going to hinge on precise
definitions of some technical terms. I think before getting into it,
I would like to list some of those terms and see what others think
they mean.
--------------------------------------

Harmonic Distortion

Intermodulation Distortion

Distortion (the unqualified word, note)

MSE (Mean Squared Error)

---------------------------------------

Having defined the terms, then what does it mean to say that a signal
has "harmonic distortion"

It's interesting to note that most of the "pre-digital era" harmonic
distortion analyzers work by nulling out the fundamental and then
measuring what's left.

Another way to do it would be to have a very good comb filter bank and
pass all the harmonics and only the harmonics and measure the result.

The first method measures THD+noise, while the second would presumably
measure only THD.

Suppose we applied the second method to Figure 9 at:
http://www.cadenzarecording.com/dither.html

What would we measure?

Would it be harmonic distortion?