In article , Ian Iveson
wrote:
Jim Lesurf wrote:

The cd-player source argument is a red herring, surely?

Not sure what you mean. It was one of the domestic sources used
purely as an example of the kind of signal source normal users will
be rather more likely to be listening to than a test-bench squarewave
generator.

I mean that the cd player is irrelevant because no-one would use one
now, or then, as a source for a square wave test.

I agree. *That* is why I use one for the page to *show* that the results in
normal domestic use are *not* what you might expect from just seeing tests
done with a bench generator. :-)


Listening to square-wave generators was no more common then than now,
either, so there's another red herring.

Agreed again. But the page is looking at squarewaves on the basis that
bench squarewaves have been used, do have uses (if correctly applied and
interpreted) but are *not* the situation in normal use.

Especially combined with the arbitrary example of a 5k square wave.
1k would give you plenty harmonics, especially if you weren't daft
and used a proper source.

Erm, the point isn't just having 'plenty of harmonics'. It is the
finite bandwidths, slew rates, current demands, etc. And how these
can be somewhat different for ordinary domestic examples than for a
bench test of the kind that was once routine.

I can't quite see how those two sentences fit together, or what you
intend to mean by either of them.

Sorry if that wasn't clear. Hopefully the other comments here since
may make it clearer.

Note that 1k as the value is also 'arbitrary' just as is any other choice
of frequency. For the same reasons which you give.



What I meant was that, when you argue that a cd source can only
accomodate one of the odd harmonics necessary for a decent 5k square
wave, it can support nine odd harmonics of 1k, which is plenty for a
quite good 1k square wave, and a half-decent generator that could be
easily acquired by a reviewer will likely offer a squarer square wave
than one used by reviewers or DIY-equipped readers in the past. In
short, the quality of the source appears to me to have no bearing
whatsoever on the demise of the square-wave test.

The key here is to consider the rate of change of the 'squarewave' source.
That isn't very dependent on the choice of waveform frequency. It is mainly
determined by the bandwidth of the source.

Then note that for a bench generator the source may have a bandwidth much
wider than that of the amplifiers being tested. But domestic sources may
well have a smaller bandwidth. Thus meaning that results using a bench
generator (at either 5k or 1k) will tend to differ from results using a
source like a CD player, FM radio, etc.


When did it become common for 'scopes to have memory? Perhaps it
then became unnecessary for the pulse to be repetitive.

IIRC I started using storage scopes back in the 1970s, and also had
waveforms with pulsed/burst patterns with long gaps, etc. But that
was for other kinds of work. I don't think that was common for things
like audio mag reviews at the time.

But did they become so? What do mags use now instead?

Pass on that as I've not had direct access to any magazine's equipment.
However so far as I know that has always varied from mag to mag, and in
appropriate cases from reviewer to reviewer. Indeed, in days of yore one
basis for choosing a specific person to do a review was that he had some
useful item of test kit. Think of Angus Mckenzie, Martin Colloms, Gordon
King, etc.

FWIW When I make measurements I tend to either use some simple kit I
own or borrow special items via my old Uni research group. That gives
me the advantage of having quite a lot of fancy kit potentially
available. Provided it isn't in use and I can get the kit and the items
to be measured in the same place for long enough!

[snip]

Consequently, interest in abstract technical tests was becoming less
common just as the capabilities of the test equipment was rising. The
classic story of alienation, I suppose. People want nice pictures. Most
of all, they want spectacular destruction testing in exotic locations.

Don't you find it soul-destroying writing for HFN?

Not really. Over recent years they did publish a number of technical
articles and 'historic' ones I wrote that I was pleased to get printed
there. (Now all on the website.) More recently they have backed away from
so much 'hard sums' for fear that graphs may upset/bore some readers. But
in fact the current arrangement suits me quite well.

At present I tend to write a 'not quite monthly' page as an 'opinion'. But
I can often link this with some detailed technical analysis or measurements
which I put up on my websites. That means that when I do get measured
results or finish an analysis I can actually put it up on the web without
having to wait some for some months *after* magazine publication. That
actually takes move than six months delay out of being able to present what
I have done. And presumably on the web it has a wider audience. Then
the magazine page tells readers where the 'meat' can be seen and they
can choose to read it if they wish.

Yes, I would like HFN (and other mags) to move back again to having some
more technical content in ways that inform readers and empower the readers
to understand results and apply them to their own circumstances. But they
aren't my magazines and I'm not the editors or publishers. I have to accept
they aren't published just for me, but for a range of readers whose views
and interests often aren't identical to mine.

Again, that seems fair enough to me. I tend to prefer reading magazines
where the content often *doesn't* simply give the views I already may hold.
No point in just reading what you already think or agree with. To learn and
discover means being willing to read what you find suprising, odd, or even
crazy. Bit like usenet... 8-]

FWIW - As mentioned in HFN this month - my favourite editor use to be John
Campbell of 'Analog'. This was because I usually strongly disagreed with
him... and then had to think carefully as to *why* I did. Sometimes
changing my views, sometimes finding new reasons why and flaws in the
arguments he presented. if you ever read his editorials you know how
infuriatingly good he was at coming up with plausible sounding arguments
for all kinds of extreme or weird ideas. As well as his ability to rip tosh
to shreds by applying rational and logical approaches.

In the end, though, the magazines will publish what they think readers
want. So if anyone wants the content to change, they do have to buy the
magazine *and* write to it giving their views on what they like/dislike.
One people don't buy they become ignored, leaving the content to be aimed
at those who *do* buy it.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html