"Don Pearce" wrote in message
...
On Tue, 22 May 2007 09:33:16 +0100, "Serge Auckland"
wrote:

Are there many distortion analysers any more that simply null the
fundamental and display the sum of the rest?

d

--
Pearce Consulting
http://www.pearce.uk.com

Most if not all of the legacy distortion analysers will be of the nulling
sort, and lab test gear has a very long life so I suspect (but don't know
for sure) that a very high proportion of distortion analysers in regular
use
are still of that sort. Today's sales of test equipment are relatively
very
low. Studios and broadcasters rarely buy new audio test gear as they
already
have instruments for their remaining analogue stuff, and all this new
digital stuff either works or it doesn't, and anyway, if it goes wrong it
needs someone from the factory to come and see to it. When I worked for an
audio test equipment manufacturer some 10-12 years ago, it was by then
already clear that very little new audio test equipment was being sold. I
think we made more money from the recalibration charges on the existing
installed park than from selling new equipment.

OK. Kind of surprising, though, as just about everybody now possesses
a distortion meter at least as good as a nulling type. I'm talking
about a PC sound card, of course. Just needs suitable software.

d

--
Pearce Consulting
http://www.pearce.uk.com

I have two conventional nulling THD meters and of course a sound card and
software. However, for THD measurements 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, you need a millivoltmeter in parallel with the
sound card input to make sure the level stays when it should. Then, with
software, I never really know what it's measuring and finally, unless you
have a suitable sound card and sample at 192kHz, you can't measure over the
100kHz bandwidth that most THD meters manage. 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. For that the
software's great but for lab work, I prefer dedicated instruments.

S.



--
http://audiopages.googlepages.com