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New page on Squares waves and amplifier performance

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
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New page on Squares waves and amplifier performance

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
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New page on Squares waves and amplifier performance

On Sun, 10 Jan 2010 18:30:55 +1300, Mike Coatham
wrote:

Jim Lesurf wrote:
Hi,

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.

During a tidy up I found a 6 page article on "Square Wave Testing of Audio
Amplifiers" in the NZ publication - Radio & Electrical Review - of August
1955. In it, it goes on to describe the testing of amplifiers using square
waves as a relatively new process. :)

And just to show that that the more things change the more they stay the
same, the article also says - and I quote "Now when we have a number of
amplifiers whose specifications, as outlined , indicate such excellent
performance, one might legitimately expect, when listening tests are
conducted, using identical programme material, and the same pick-up and
speaker system, that all the amplifiers sound the same. It was with
considerable surprise that we found exactly the opposite. "

They did tests on 7 un-named amplifiers and included oscillograms of the
amplifiers at 30hz, 400hz & 10,000hz.

The conclusion reached was that square wave testing "can help sort the
sheep from the goats. With all its advantages, this type of test will still
not give an unambiguous answer to the 40 dollar question ...Will this
amplifier sound well on music?. It will give the experienced worker a
pretty good idea of where his designs could be improved, and it seems that
the very best amplifiers do give very similar square wave results. Where
faults are apparent, the test shows them up much more clearly than any
other method, and will also indicate fault conditions that cannot readily
be discovered at all in any other way."

So here we are, 55 years down the track and its deja vu all over again :0

Mike

No chance of scanning it and making it available, is there? That would
be interesting.

d

New page on Squares waves and amplifier performance

David Looser wrote:
"Trevor Wilson" wrote

**Red Book CD tops out at 22.05kHz. A decent RR can easily top
30kHz. A top of the line vinyl rig can easily manage 60kHz. Do the
math.

And what do your ears top-out at?

**Let me go back to the original claim:

**If you REALLY want to laugh, look at a 7kHz square wave from a CD player
(even 5kHz is barely passable from most CD players). A good R-R or high end
vinyl playback can do a MUCH better job.

Clear enough?

I said nothing about audibility, or not. I was SPECIFICALLY referring to the
square wave capability of the different formats. I was careful enough to
specify the frequency too. MY ears are not under dicussion. The relevant
performance of the cited formats is.

--
Trevor Wilson
www.rageaudio.com.au

New page on Squares waves and amplifier performance

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

New page on Squares waves and amplifier performance

In article ,
bcoombes
bcoombes@orangedotnet wrote:

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. :)

I can confirm they did. Partly because I have a bookcase full of old
issues of HFN just beside me as I type. Also because I was working on
developing power amps at the time 'TIM' appeared on the scene and
there was a brief flurry of panic until people realised it was a
'problem' that decent design solved with trivial ease.

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.

Back then square wave tests were probably more relevant for two reasons.

One was that more HiFi enthusiasts were knowledgeable about technical
matters so were better placed to judge what such results might tell them.

The other was that aspects like peak current delivery, slew rates, etc were
more likely to be inadequate as the devices available were more limited.

However the passage of time has changed both of those factors! Although I
do still wonder about some modern 'high end' designs. What peak current and
slew rates can they provide, and is it adequate for real use with music
into speakers? In particular I wonder about some valve designs. At what
current do they limit, and what happens when they do?... Alas, if no one
measures this you can't tell, or often even guess with any reliability.

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

New page on Squares waves and amplifier performance

"Trevor Wilson" wrote

I said nothing about audibility, or not. I was SPECIFICALLY referring to
the square wave capability of the different formats. I was careful enough
to specify the frequency too. MY ears are not under dicussion. The
relevant performance of the cited formats is.

Whilst it is possible to line up analogue tape machines to give a 30kHz
bandwidth, that is at the expense of in-band flatness and distortion. I've
seen the results of recording squarewaves on professional tape recorders,
and the results aint' pretty! In any case we are talking about expensive
studio machines here, the relevant comparison would be to 96 and 192kHz
sampled audio, which clearly has a far greater bandwidth.

As for vinyl, a typical minimum groove radius is 6cm. That means a linear
velocity of about 210 mm/sec. So the wavelength of a 60kHz signal is
..0035mm. What is the sidewall contact area of even the smallest stylus?

David.

New page on Squares waves and amplifier performance

Well, obviously, in the days I was talking about, digital recording was
still in the domain of the pro, and tended to sound very furry by comparison
to good analogue.

However I remember having a bit of a heated argument about the realism or
otherwise with some test luminary at a Heathrow Hotel show back then.
Pointing out that the dc coupled amp was a complete waste of time as
speakers could not really do constant air pressure unless you lived inside
an infinite baffle enclosure in any case.
I agree crossovers by their design had phase shift, after all they are
basically fillters.

I then got into some heated discussion about doppler with a lowther
enthusiast..

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!
"Trevor Wilson" wrote in message
...

"Brian Gaff" wrote in message
om...
We used to use squarewaves for the following.
To show how bad tape machines were...
To show the tone control effects

However, you need to look at the harmonics on a true square wave, which
of course cannot actually exist.

**If you REALLY want to laugh, look at a 7kHz square wave from a CD player
(even 5kHz is barely passable from most CD players). A good R-R or high
end vinyl playback can do a MUCH better job.

--
Trevor Wilson
www.rageaudio.com.au

New page on Squares waves and amplifier performance