[sdiy] Better testing techiques for audio circuits

[David G Dixon]

> > However, I find that it does capture a lot of the common nuisances, 
> > like spurious oscillations, etc, and it does predict the 
> THD of sine 
> > shapers and things with remarkable accuracy.
> 
> I'd be interested in how you confirmed the accuracy.  Did you 
> run the real circuit into a distortion analyser?

Yes.  Multisim predicts the THD of a sine shaper when the transistors are
perfectly matched (as Harry mentioned earlier, the SPICE models of
transistors are ideal).  In real life, this tends to be the minimum
attainable THD.  You can turn on "Use component tolerances" but this doesn't
always give very realistic results.  My attitude is, design for the ideal
case, but ensure that you can live with the variances, and use precision
components when you really need them.  You get an interesting perspective on
component tolerances when you tune and calibrate 120 VCOs!

In any case, I think that absolute values are meaningless with this sort of
stuff.  What I'm looking for are relative values (for component
optimization, for example), and Multisim (or any SPICE model) is perfect for
this.