"bcoombes" bcoombes@orangedotnet wrote in message
o.uk...

Ah yes bit's all coming back to me now, there were a bunch of us at work
who were 'into hi-fi' and we'd spend much time studying the slew rate
figures from various amp tests and then deciding which one we'd like to
own. ISTR that Radford amps were the ones to die for back then.

They still a-)

Iain

bcoombes wrote:

You conclude that reviewers have abandoned the square
wave, but did they ever use it much anyway?

Without in anyway claiming to be an expert on these things
I vaguely seem to remember that most amp tests in the
HI-Fi mags of the 1970's and 80's had a square wave read
out printed somewhere in the test. I also *seem* to
remember these were at 1k ...but of course these are
distant and increasingly dim memories.

Could be...I only started looking in the 90s. I did have
some passing interest much earlier but memories are very dim
indeed. I have the impression that older hi-fi mags commonly
expected a narrower, more hands-on and informed audience,
and I guess some mags continued to address that audience
even when it had mostly disappeared.

The likes of Hi-Fi News now pander to the ignorant by merely
convincing them they've learned something, which apparently
is not hard to do. It no longer needs to be useful, because
readers won't actually use it. They also pride themselves on
posh purpose-designed test sets that produce nice
print-ready pictures. There's not much titillation in a
square wave.

It could also be that the kinds of problems highlighted by
square wave testing are no longer issues. How much variety
would be apparent in comparing square wave tests of various
audio amps these days?

Ian

Ian Iveson wrote:
bcoombes wrote:



The likes of Hi-Fi News now pander to the ignorant by merely
convincing them they've learned something, which apparently
is not hard to do.

As you can see in recent threads see I'm not a subscriber to the view that
everything that needs to be known about audio is known, on the other hand when
I read a review that calls an amp an "urgent and frisky sounding musical tool"
(Decembers Hi-Fi World) I can't help chuckling and wondering who the 'tool'
really is.

In article ,
bcoombes

As you can see in recent threads see I'm not a subscriber to the view
that everything that needs to be known about audio is known, on the
other hand when I read a review that calls an amp an "urgent and frisky
sounding musical tool" (Decembers Hi-Fi World) I can't help chuckling
and wondering who the 'tool' really is.


My favourite from many years ago was an amplifier review that said the amp
was 'chocolate sounding' and 'made the singers sound like they were raised
up above the ground'. The problem with such descriptions is that I have no
idea how they would relate to anyone else than the reviewer, using any
other system, room, etc.

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

In article , Ian Iveson
wrote:
bcoombes wrote:

You conclude that reviewers have abandoned the square wave, but did
they ever use it much anyway?

Without in anyway claiming to be an expert on these things I vaguely
seem to remember that most amp tests in the HI-Fi mags of the 1970's
and 80's had a square wave read out printed somewhere in the test. I
also *seem* to remember these were at 1k ...but of course these are
distant and increasingly dim memories.

Could be...I only started looking in the 90s. I did have some passing
interest much earlier but memories are very dim indeed. I have the
impression that older hi-fi mags commonly expected a narrower, more
hands-on and informed audience, and I guess some mags continued to
address that audience even when it had mostly disappeared.

Yes. If you compare issues from the period, say, before the mid 1970s and
nowdays the differences are quite stark. Back then it was routine to
publish quite detailed technical articles and to assume many readers could
at least solder, bend tin, and follow the gist of some equations, graphs,
etc. And so able to understand and decide for themselves the meaning of
such data.

Now the measured parts of reviews tend to be in a small boxout and often go
without any real explanation to allow readers to assess what they might or
might not be able to tell them.


It could also be that the kinds of problems highlighted by square wave
testing are no longer issues.

I suspect that depends on the items in question. So taking the example of
power amps I'd expect that most 'well designed' power amps in recent
decades would show no problems, and all a squarewave test would do would be
to confirm the bandwidth and any presence of an output network.

Alas, the snag here is my qualifier 'well designed'. It would not surprise
me if some of the more 'high end' products would reveal a set of problems.
Slew rate and/or current limiting for one. Possible also stability or other
problems.

This is because I have the feeling that some makers and designers may
simply be living on the fact that there may be problems which the review
methods used these days simply don't show up. Hence relying on the item
seeming OK in the system/circumstances/judgement of a few reviewers and
there being no info provided that readers could use to warn if in *their*
circumstances the amp might not work so well.

This is a general concern I've had growing uncomfortably for some years
now. So the lack of squarewave tests is just one perhaps minor aspect of
this wider possibility.

How much variety would be apparent in
comparing square wave tests of various audio amps these days?

Good question. :-)

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

In article , Ian Iveson
wrote:
Jim Lesurf wrote:

I've just put up a new web page at

http://www.audiomisc.co.uk/HFN/Squar...quareDeal.html

that looks at the use of squarewaves for assessing amplifiers, etc.

Prompted to do this by noticing squarewave results being used to
present ideas about speaker cables, and realising that the humble
squarewave has largely fallen into disuse.

I've also tweaked the site a bit, and hope to make a few other minor
improvements and alterations soon.

Slainte,

Jim


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.

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.

Also, as mentioned in the preamble, this was prompted by looking at
material on loudspeaker cables of tests using bench sources which brought
to my mind the way similar things were done in the past in reviews, etc.

You conclude that reviewers have abandoned the square wave, but did
they ever use it much anyway?

Yes. It was very common a few decades ago in most HiFi mags. Have a look at
Hi Fi News or similar back in the 1960s/1970s for example.

I think Stereophile still have some squarewave tests. IIRC I've seen them
in issues in the last year or two. But they have essentially vanished from
UK magazines.

A square wave test result seems to me
several levels of abstraction distant from what the average audio
enthusiast might be interested in. It offered a convenient method of
testing amplifiers for designers or home builders with limited
equipment. It was never ideal because it superimposes several tests
such that results need careful interpretive disentanglement.

I agree.

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.

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

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.
It's not as if suitable sources are no longer available or
inferior to what they were, so what could the source have to
do with the disappearance of the test?

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

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.

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.

Also, as mentioned in the preamble, this was prompted by
looking at
material on loudspeaker cables of tests using bench
sources which brought
to my mind the way similar things were done in the past in
reviews, etc.

You conclude that reviewers have abandoned the square
wave, but did
they ever use it much anyway?

Yes. It was very common a few decades ago in most HiFi
mags. Have a look at
Hi Fi News or similar back in the 1960s/1970s for example.

I think Stereophile still have some squarewave tests. IIRC
I've seen them
in issues in the last year or two. But they have
essentially vanished from
UK magazines.

A square wave test result seems to me
several levels of abstraction distant from what the
average audio
enthusiast might be interested in. It offered a
convenient method of
testing amplifiers for designers or home builders with
limited
equipment. It was never ideal because it superimposes
several tests
such that results need careful interpretive
disentanglement.

I agree.

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? It
does seem that storage 'scopes were becoming common around
the time that square wave tests began to wane. Storks and
babies, maybe, not directly related but both linked to a
common theme. Hands-on engineering experience became less
common as machines became more complicated. 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?

Ian

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

All very tuue. I suspect the design of the pulse itself will be next on the
agenda then. If a pulse of no rise or fall time could be made presumably it
would be silence if it had nil dwell time as well? grin.

One needs to design one shot and multi shot tests to allow the scope to see
what is going on, as listening to pulses all the time is hardly any kind of
way to go!

In any case, do you use plus only, or plus and minus pulses?
I seem to recall one weird amp from Sinclair I saw which had apparently
perfect results, but sounded absolutely terrible and radiated RF like a
power line adaptor, but you know what he was like!

The idea I think was to fast switch the output and use the duty cycle to
create the output, so small devices could be used. Trouble was that this
needed massive amounts of low pass filtering to get it to really work..
Ho hum.

Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
"Ian Iveson" wrote in message
...
Jim Lesurf wrote:

I've just put up a new web page at

http://www.audiomisc.co.uk/HFN/Squar...quareDeal.html

that looks at the use of squarewaves for assessing amplifiers, etc.

Prompted to do this by noticing squarewave results being used to present
ideas about speaker cables, and realising that the humble squarewave has
largely fallen into disuse.

I've also tweaked the site a bit, and hope to make a few other minor
improvements and alterations soon.

Slainte,

Jim


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

You conclude that reviewers have abandoned the square wave, but did they
ever use it much anyway? A square wave test result seems to me several
levels of abstraction distant from what the average audio enthusiast might
be interested in. It offered a convenient method of testing amplifiers for
designers or home builders with limited equipment. It was never ideal
because it superimposes several tests such that results need careful
interpretive disentanglement.

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

With a single pulse and a 'scope with memory to capture its consequences,
the entire transient response, HF and LF, can be seen, without
interruption by successive pulses.

Ian

On Sun, 10 Jan 2010 10:37:28 GMT, "Brian Gaff"
wrote:

The idea I think was to fast switch the output and use the duty cycle to
create the output, so small devices could be used. Trouble was that this
needed massive amounts of low pass filtering to get it to really work..
Ho hum.

It was Class D - used in just about every subwoofer you can buy today.
So it turned out ok in the end.

d