[sdiy] Better testing techiques for audio circuits

[David G Dixon]

> Then you mention your mixer having <0.0007% THD.  Its 
> unlikely that you'd be able to simulate to that extreme in 
> SPICE.  To measure it in the real world needs expensive kit 
> (Audio Precision 2700 series). 

I use Multisim, which is a SPICE-based simulator package from NI, and the
THD tool doesn't even have a fourth decimal point -- it only goes down to
0.001%.

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.