New page on Squares waves and amplifier performance
 

On Sun, 10 Jan 2010 20:30:46 +1100, "Trevor Wilson"
wrote:

**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.


Ok, I'll bite. Here's a 7kHz square wave as produced by a CD.

http://www.soundthoughts.co.uk/look/7ksquare.png

I'm not laughing - I call that a pretty damn perfect piece of audio.

Meanwhile, the nearest I could find for a cartridge was this at 1kHz -
an immensely easier job, and yet still barely handled by a V15.

http://gallery.audioasylum.com/cgi/v...&w= 641&h=607

I'm going with the CD, thank you.

Meantime, will you please post your 7kHz vinyl waveform? I need to
make a true comparison.

d

New page on Squares waves and amplifier performance
 

But this only proves how false a squarewave is. Lets take another tack. Does
the brain actually hear a square wave?
The answer has to be no, as we are using mechanical devices to transfer the
pressure differences from an electronic signal to the brain, and if there
is already no such thing as a rise time and fall time of zero, then in a
room with speakers with mass and all the implications of air compression
and the ear drum, another mechanical device, the heard shape is going to
probably be more like a sine wave with some harmonics at audible
frequencies.


Has anyone actually built an artificial ear and processor, remembering of
course the inherent nonl linearity of the way the signal is processed, and
of course the amazing echo nulling out of the ears/brain system!

If you do do this, you actually still cannot listen to it, only look at it,
as we do not, yet, have a gold plated phono input to our brain.

Brian

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"Trevor Wilson" wrote in message
...
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
 

Now, don't get all hot about it.
I have a dbx recorder or two here, and one can actually record bandwidth
limited squarewaves at higher levels. The one artefact you tend to see of
cours, is down to the finite time the processor takes to do things. You tend
to get level overshoots and undershoots and an obvious worsening of the
noise performance on louder recordings
I never really understood why everyone went toDolby, it was terrible if the
heads and eq were not exact, and was inherently non linear in an obvious
way. I would imagine if DBX had been adopted more widely, people would have
been a lot happier to have cassettes for home recording.

Brian

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"Phil Allison" wrote in message
...

"Trevor Wilson"

**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.


** Square waves output from a CD player (with a suitable test disk) are
near perfect examples of audio band limited square waves. The amplitude
and frequency are steady as a rock, harmonic phase relationships are near
perfect, channel matching is perfect and only inaudible harmonics are
missing.

OTOH, the square wave performance of typical hi-fi R-R and cassette decks
is utterly woeful. Amplitude is modulated all over the place, there is wow
and flutter, channel matching is woeful, there is obvious tape noise,
harmonic phase relationships are all out of wack, there is obvious ringing
and still the inaudible harmonics are missing.

In the cases of both LP and cassette, it is only possible to record a
square wave with low amplitude ( ie -20 dB or so) with any hope of just
getting the available bandwidth.

With CD, it makes no difference - full level ( ie 0dB) square waves are
routine.

TW is bereft of even a single clue.



.... Phil

New page on Squares waves and amplifier performance
 

Brian Gaff wrote:
Now, don't get all hot about it.
I have a dbx recorder or two here, and one can actually record bandwidth
limited squarewaves at higher levels. The one artefact you tend to see of
cours, is down to the finite time the processor takes to do things. You tend
to get level overshoots and undershoots and an obvious worsening of the
noise performance on louder recordings
I never really understood why everyone went to Dolby,

I remember when Dolby B first started appearing on cheaper Japanese cassette
players. It solved the hiss problem by simply slicing off everything above 8k.
Of course these days that wouldn't bother me...unfortunately :(

New page on Squares waves and amplifier performance
 

Why cannot you just present your arguments and stop slagging others off a
bit, and we might just understand waht you really mean.
Basically, the replay head reacts to changes in magnetic flux, thus
whatever you record, only the changes can be read. Many portable machines
use a permanent magnet to erase the tape. DC if you will, but all you hear
if you replay it is the sound of the tape bumping about as it passed the
erase head.


Of course most tape machines use ac to erase and also to bias the magnetic
material to a more linear part of its flux curve between saturation and the
non linear low end.

If you listen to cheap recorders with dc bias, not only are they noisier
due to the dc,and bouncing, but only have half the dynamic range.

I take issue with you about what a square wave is.

If, for example you had a square wave with a 3v p to p level, and the zero
in the middle, then you have plus and minus 1.5. If you had a frequency
variation on it and made each cycle half an hour long, you would have a psu
switching every half hour to the two polarities at 1.5 v. Of course if you
moved your zero point....

You can view a lot of things in electronics in lots of ways, as behaviour of
what you are testing is surely easier to grasp if one looks at it in an
understandable way.

I'd better not go on here, as we might start talking about speaker cables..
Brian

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"Phil Allison" wrote in message
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"Brian Gaff"


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.

** Huh ???????

Response down to DC is not a requirement for flat topped square waves !!!!

Square waves are NOT " little bits of DC " as fools like YOU think !!!!


You did not cover this aspect,


** Good thing he did not - since it would have been total ********.

For god's sake, learn some electronics - you damn fool.



.... Phil

New page on Squares waves and amplifier performance
 

"Brian Gaff" wrote in message
m...

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.

When was that then?

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.

The point of dc coupled amps was never to get dc from the speakers! Anyway
living inside an infinite baffle enclosure would still not make a point to
it as there is an air path through the mouth to the back of the eardrum, so
our ears are not "dc coupled"

The point of dc coupling amplifiers was to reduce LF phase-shifts, thus
increasing LF stability within feedback loops, and to eliminate bulky and
expensive output capacitors.

David.

New page on Squares waves and amplifier performance
 

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

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"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

New page on Squares waves and amplifier performance
 

"Brian Gaff" wrote

I never really understood why everyone went toDolby,

Well Dolby came first!

it was terrible if the heads and eq were not exact, and was inherently
non linear in an obvious way. I would imagine if DBX had been adopted more
widely,

I never liked DBX, noise modulation was far too apparent for my liking.

people would have been a lot happier to have cassettes for home recording.


I fail to see how cassettes could have been *more* popular for home
recording than they were! People, by and and large were very happy with it.

David.

New page on Squares waves and amplifier performance
 

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

New page on Squares waves and amplifier performance
 

Well, I suppose the misleading part of all this is actually calling them
square waves in th first place, as has been noted these do not exist.
There are other forms that can be used of course, the one sided square, with
a leading slope but a fast drop, and the inverse of this.
Then there are triangular waves of course, which sound almost as bad as
square waves.

I think the listening tests do prove some things though. Firstly, nobody is
really sure what 'right' actually is, so an amp may sound bad, but it might
be actually more accurate than one you like.

It is interesting sometimes to put a scope on the psu when an amp is running
too, often some frequencies exist at quite high levels, despite all the
decoupling in the world being there, indeed, decoupling itself can make an
amp sound leaden.

In the complexity of the audio and all the bits in the chain to how the
brain perceives the whole is still not well understood, I feel.

However, I do not think that most speaker wire tests are actually testing
the wire...

Brian

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"Don Pearce" wrote in message
...
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