[sdiy] Order analysis

[cheater00 .]

Hi guys,
when browsing through the Stewart of Reading catalogue as per Neil's
suggestion, I've found out about a really cool way to analyze
non-linearities called "order analysis". It lets you separate
non-linearities that are frequency dependent from ones that are not.

Here's a short intro:
<http://zone.ni.com/reference/en-XX/help/372416A-01/svtconcepts/intro_ord_ana/>

Basically, you make a sweep, say a sinewave from 10 to 1000 Hz, and
put it through your DUT. Then you un-sweep the output, that is you
pitch shift it so that the sine wave in the output is at a constant
frequency rather than sweeping. Finally, you do a spectral analysis.
Harmonics that are constant in amplitude are not frequency dependent,
harmonics that change in amplitude are frequency dependent. I've never
heard of this, but I can see immediate usability in a lot of fun audio
circuits.

Cheers,
D.

(at first I'd thought Order Analysis was something for timekeeping at
a service centre...)