"Serge Auckland" wrote in
message

I rarely use the sound card as it is too difficult to use
. Firstly you need an attenuator to reduce the incoming
level, as few soundcards take more than a couple of volts
of input before clipping themselves, idealy

A 5K 2 watt high quality potentiometer suffices.

you need a
millivoltmeter in parallel with the sound card input to
make sure the level stays when it should.

You mean a voltmeter across the UUT output. We often used those with the old
nulling-type analyzers for one reason or the other.

Then, with software, I never really know what it's measuring

That's your fault - a good experimentalist should be able to determine that
with a few real world measurements. On a bad day, analyze some signals
generated for the purpose. Generating complex tones is very easy these days.

unless you have a suitable sound card and sample
at 192kHz, you can't measure over the 100kHz bandwidth
that most THD meters manage.

Virtually every sound card that I'd consider to be an alternative to test
equipment samples that high.

I use the software test set
for analysing WAV files. For example, it's easier for me
to take my laptop to the hi-fi than test gear, so if I'm
making any measurements to my room or system, I will
record the DUT as a WAV and analyse it later.

Agreed - it is easy to capture data in the field, and analyze it in detail
later on.