[sdiy] Measuring Audio Sine Purity

[John Speth]

> How would a DIY person measure the purity of a sine wave beyond using a
> spectrum analyzer?  To give a figure of sine purity, of distortion
(THD?) ?

The pros use Audio Precision tools which are considered to be the standard
for THD measurement devices.  The AP boxes are outboard to the PC.
They're connected digitally to the PC eliminating the audio inaccuracies
introduced by the PC.  My guess is that if PC sound cards were comparable
to the AP boxes in audio quality, the AP boxes wouldn't be needed.

You might find PC sound card analysis software but I'd be concerned about
the accuracy at the low levels of THD that you probably want to measure.

JJS