"Pooh Bear" wrote in message
...


Bret Ludwig wrote:

Arny Krueger wrote:

An experienced eye ( such as mine ) can interpret the waveform
rather
well.

This is bull**** incidentally. Oscilloscopy is not the tool to track
down non-gross distortions, at least not directly.

You incorrectly attributed that comment.

It was mine ! And I stand by it ! Very much so in fact.

And, I agree with the idea that looking at the output of a THD analyzer with
a scope is a good way to look at *all* forms of distortion, not just
crossover distortion.

Examination of the distortion analyser output waveform shape is highly
valuable
with regard to getting a feel for the harmonic content and indeed any
specific
linearity issues. Crossover artefacts are very obvious too. You simply
'get an
eye' for it.

Agreed. The THD analyzer's output is pure distortion, with the fundamental
removed. This greatly enhances the sensivity of the 'scope as a distortion
analysis tool.

That's the whole point of a THD analyzer - remove the fundamental.
Operating a THD analyzer is composed of setting levels and nulling out the
fundamental with a frequency control and a balance control. With some
practice one develops a natural ability to turn the right knob in the right
direction by simply glancing at the scope.

BTW Graham, it looks like Bret just admitted what a complete ignoramous he
is about audio testing. Using a THD analyzer is a canonical tool - if you
haven't been there, you haven't been!

You *could* use a spectrum analyser to get the numbers but a waveform on a
scope
take some beating for instant 'readability'.

Looking at nonlinear distortion with a spectrum analyzer is a completely
different experience. It's probably more of an intellectual experience as
opposed to the hand-and-eye coordination that one develops while using a THD
analyzer with a 'scope.

I guess 25+ yrs of doing this for real as a design professional gives me
the
advantage over the casual newsgroup junkie !

Exactly. I first obtained hands-on experience with a THD analyzer in the
mid-1960s, which is now about 40 years ago. It was the Heath vacuum tube
model, and I was as an undergraduate engineering student. The object of my
measurements was a RIAA phono preamp that I designed as a junior-year
project. After the Army I returned to school and found they had upgraded to
a HP 331 with auto-nulling. The auto-nulling was slower than the trained
hand, but it could speed the process, nevertheless.