[Amps] K8RI's discussion 12/27/2011 ref Linear Amplifer Tuning - PROPERLY

[Gene May]

I am also interested in audio HiFi design, and have wondered why some IM tests for products in that field use three (non-harmonically related) frequencies, while most only use two.  Using three well-spaced frequencies should greatly increase the chance that IM signals will be detected, since there is a greater chance that such frequencies wouldn't get filtered out.  I suppose that the reason that some still use only two frequencies, of course, is that with properly selected frequencies one can hide one's product's poor linearity.
 
Frequencies of 400, 500, 900, 1100, 2300 and 2600 Hz to a mike input should provide a particularly good test, although the signal generator would be more complex than the usual.  An audio clipper following these frequencies would probably show a mess.
 
TNX,  Gene May
WB8WKU