New page on Squares waves and amplifier performance
 

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.

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

--
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
 

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.

grin

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!
"Jim Lesurf" wrote in message
...
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.

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

--
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
 

Actually, having read your piece, I suppose I should mention some other
things. Some of the edgy sounding amps in the 70s were often due to dodgy
filtering from what I could tell. Pioneer seems to suffer from this
problem.

I once had a Tandberg amp that really seemed able to drive almost anything,
and sounded crisp and nice. Problem was it picked up any RF going and
amplified it.. Not very practical.


Tape, as I said in another response here had problems as it was obviously
impossible to record DC to a tape, so the flat tops were not flat.

You did not cover this aspect, but when folk decided direct coupling was a
nice way to sell amplifiers, they used to show it with square waves of
course. However, in air, you do not get DC, unless you cont the wind as DC,
but I've yet to see any speaker capable of a sustained draft!

So, integration will occur, thus the square wave is an input that cannot be
output in any case.

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!
"Jim Lesurf" wrote in message
...
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.

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

--
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
 

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

New page on Squares waves and amplifier performance
 

In article ,
Brian Gaff wrote:
We used to use squarewaves for the following.
To show how bad tape machines were...
To show the tone control effects

You can also use them to show up the lousy phase response of most
loudspeakers. :-) Although by the same token they also show the Quad ESLs
are rather good in this respect.

However, you need to look at the harmonics on a true square wave,

Not sure which purpose you have in mind. You can of course use either time
domain or frequency domain depending on what your specific purpose may
"need".

which of course cannot actually exist.

Yes, that is something I point out on the webpage, and explore the
practical implications. One being that tests with bench waveform generators
may give different results to normal domestic audio sources. :-)

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
 

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?
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?

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. :)

New page on Squares waves and amplifier performance
 

In article , Brian Gaff
wrote:
Actually, having read your piece, I suppose I should mention some other
things. Some of the edgy sounding amps in the 70s were often due to
dodgy filtering from what I could tell. Pioneer seems to suffer from
this problem.

I once had a Tandberg amp that really seemed able to drive almost
anything, and sounded crisp and nice. Problem was it picked up any RF
going and amplified it.. Not very practical.

That kind of thing is an example of why I and others came to regard it as
sensible to use passive RC filters on the inputs and output networks. It
not only helps define the maximum slew rate demanded of the amp. It also
helps prevent RF entering via input or output.


Tape, as I said in another response here had problems as it was
obviously impossible to record DC to a tape, so the flat tops were not
flat.

You did not cover this aspect, but when folk decided direct coupling was
a nice way to sell amplifiers, they used to show it with square waves
of course.

Yes. IIRC People like Harmon Kardon were keen on this and a 'dc to light'
approach. Not an approach I personally have been very keen on.

However, in air, you do not get DC, unless you cont the wind
as DC, but I've yet to see any speaker capable of a sustained draft!

Well the air *pressure* will certainly show variations with a spectrum well
below, say, 1Hz. But I'd agree that has little to do with normal audio
meant for human beings. :-)

So, integration will occur, thus the square wave is an input that cannot
be output in any case.

As the page (and your earlier posting) have already said, yes, you
inevitably have an upper limit and finite response time. The situation with
dc is less clear as you then end up worring about the meaning of 1/f noise
and how any level can be true dc if the universe only has a finite duration
of existence. However I thought that would be outwith the scope of the
webpage... ;-

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 , 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

New page on Squares waves and amplifier performance
 

In article ,
bcoombes
bcoombes@orangedotnet wrote:
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.


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. :)

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.

However as the page (and Ivan) have indicated, that was an example of how
the use of squarewaves could easily be mis-interpreted and cause people to
worry about nothing much.

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
 

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