New page on Squares waves and amplifier performance
 

"bcoombes" bcoombes@orangedotnet wrote in message
...
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 :(

Except that that's not what Dolby B does.

In playback Dolby B reduces the level of low-level HF by around 10dB. That
*should* be compensated for by an equivalent boost in HF during recording,
though if the alignment isn't good level mistracking will occur. If there
was no boost at all during recording then low-level HF, from about 3k (not
8k) upwards (but not high level HF) will be dropped in level by about 10dB.

David.

New page on Squares waves and amplifier performance
 

In article , Brian Gaff
wrote:
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.

Your objection is a tad too sweeping. Triangle waves, sinewaves, etc, also
"do not exist" if you require "exist" to mean that the real-world shape is
absolutely identical to the theoretical! :-)

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.

Alas the problem here is being expected to make sense of *someone else's*
'listening test' in a magazine when their ears, system, etc aren't yours.

The point of objective data - like ye olde fashioned squarewave test - was
to give data which could be interpreted or understood. For example showing
if there was a problem like a slew rate or max current limit that would be
too low for your own music listening in your specific situation. Thus - for
those who could interpret correctly - freeing you from having to guess what
the devil the reviewer was whittering on about when they claimed the amp
gave a 'nice chocolate sound' or whatever. :-)

The snag is that - as with many other types of measurement - they can
easily be done in an inappropriate manner, or their results totally
misinterpreted. Modern reviews generally 'solve' that problem by discarding
the idea of doing the test and trying to make sense of the results. :-)

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 , Don Pearce
wrote:
On Sun, 10 Jan 2010 10:49:43 GMT, "Brian Gaff"
wrote:

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.

If we limit the requirement to "within the meaning of the act", then
square waves are doable - to the same extent and for the same reasons as
triangular waves.

That is one of the things that I hope the webpage indicates. That the
'squarewave' needs to be in reality a practical form appropriate for a
given purpose. The snag being to assess what that means, and how to
interpet the results.

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


They certainly weren't when Ben Duncan did them...

Did you have

http://www.st-andrews.ac.uk/~www_pa/...eshift/cp.html

in mind there?... :-)

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
 

Bill Taylor wrote:
On Sun, 10 Jan 2010 10:22:12 +0000, bcoombes bcoombes@orangedotnet
wrote:

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 :(

The cassette deck might have sliced everything above 8k off, but Dolby
B didn't.

But on these decks it did because with the Dolby off there was response up to at
least 12k whereas with it on it didn't just remove the hiss it removed
everything..as per my not properly implemented comment.


With a good deck, good tape, careful alignment and a low
recording level it was possible to get a flattish response to18-19k.

I think that's Nakamichi terroritory and a few other *very* high end decks only,
certainly not cheap.

The problem was that the decks had to be carefully set up in
conjunction with the tape that was to be used, other wise the
processing exacerbated frequency response variations.

Yes my point in saying 'cheap' was that it hadn't been properly implemented

New page on Squares waves and amplifier performance
 

"bcoombes" bcoombes@orangedotnet wrote in message
...
Bill Taylor wrote:
On Sun, 10 Jan 2010 10:22:12 +0000, bcoombes bcoombes@orangedotnet
wrote:

The cassette deck might have sliced everything above 8k off, but Dolby
B didn't.

But on these decks it did because with the Dolby off there was response up
to at least 12k whereas with it on it didn't just remove the hiss it
removed everything..as per my not properly implemented comment.


What tolerance was there on the response up to12k?, and at what rate did the
response fall off above 8k with Dolby on? What level, relative to Dolby
level, did you make your measurements at?

Removing everthing above 8k wouldn't make much difference to the hiss
anyway, as audible hiss is mainly in the 2k- 10k region

David.

New page on Squares waves and amplifier performance
 

Don Pearce wrote:
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

No problem with that - I'll send you a copy later today. I'd also send Jim
a copy too before he gets on my case :)

New page on Squares waves and amplifier performance
 

"Mike Coatham" wrote

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. :)


In an advertising pamphlet from Haynes Radio that I have; undated but
probably from the late 1940s, there is the following sentence at the end of
the description of their "Quality Amplifier":-

quote
Amplifier designs are developed with the aid of a square wave-form
generator, which experience has shown will reveal defects unobserved by
tests with oscillator and distortion factor meter, and upon which quite
misleading test data might be based.
unquote

Incidentally this Amplifier (£18.10s plus £6.15s for the PSU) uses 4
triodes, including a pair of PX4s in the output stage.

David.

New page on Squares waves and amplifier performance
 

"Trevor Wilson" wrote in message

David Looser wrote:
"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.

Bull****

Agreed.

**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.

The math includes the phase response. If a system is linear phase or minumum
phase then there is a mathematical relationship between amplitude and phase.
In the general case, there is no such necessary relationship.

Modern D/A and A/D converters are generally generally based on phase linear
filters.

Both LP and analog tape playback is far from being either minimum phase or
linear phase because of their transfer function is based on both minimum
phase and non-minimum phase filtering. The minimum phase elements are
electronic, and the non-minimum phase elements are based on the fact that
they both involve moving media with mechanical and/or magnetic wavelength
effects.

Bottom line, it is not uncommon to have wide bandwidth, but with many
unpredictable phase changes. Well the phase changes are unpredictable until
you understand more details about how they work.

In general analog tape machines have far poorer square wave response than
their actual frequency response predicts because of wavelength effects
related to the head gaps.

New page on Squares waves and amplifier performance
 

"Brian Gaff" wrote in message
m

But this only proves how false a squarewave is.

Agreed.

Lets take
another tack. Does the brain actually hear a square wave?

Not at all. The nerves connected to the brain send information based on a
spectral analysis that takes place in the inner ear. No attempt is made to
represent a waveform to the brain.

Look up "The organ of Corti" for more information.

New page on Squares waves and amplifier performance
 

Don Pearce wrote:
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
Don can you e-mail me direct and I'll send you the pdf My first attempt to
get it to you got bounced.

Mike