Re: Interpreting Square Wave Traces


"Ian Iveson" <IanIveson.home@xxxxxxxxxxxxxxxx> wrote in message
news:h7UUh.30556$aB1.25527@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
Iain wrote

I still don't think there is such a thing as a square wave...especially
now that storage scopes are cheap.

Please elaborate:-)

Well, I know it's a fundamentalist position, but nothing can be both
square, and a wave, at the same time. Fundamentally, waves are not square
things.

:-)) Agreed. But this is the terminology that has been written in
stone by the God of Triodes, and his disciples, Langford-Smith,
Tremaine and Crowhurst, since the dawn of time:-) I suppose
we could talk about square traces, but most people would
probably ask: "Don't you mean square waves?"

There are also people who widely disparage the use of the term
"passive preamplifier" because it has no gain. Others argue that
the term is appropriate as it is a unit that is placed "pre" (before)
the amplifier.


From a practical point of view, a "square wave test" confuses the response
to the edge with the response to its repetition. If you have a storage
scope you can use an impulse or single step. Ideally then you can see the
complete transient response without fear of interruption. The frequency
response is better done with sine waves, for the purpose of clear
demonstration.

Non-linear behaviour is perhaps best investigated with a test specific to
its type. The more you can disentangle each from the others, the better.

The perceived need for a table of square wave responses rather underlines
the point. The more it can tell you, the more complicated the
interpretation of a test becomes.

My list of square wave pics was the result of looking at a number
of non-linear conditions in a power amp, which were then simlated
for photography using a digital processor. Like myself, I know there
are many people who have looked at a square wave, and wondered
to themselves "What does it actually mean?" (I am talking here
about people working at hobby level)

Considering the relative sophistication and precision of common modern
test equipment, surely there is a case for updating tradition?

Please start a thread. This is of great interest

Hmm. There are some areas where knowledge is no substitute for
intelligence gained from experience. I've never been inside a serious
recording studio, or had the opportunity to talk at length to the
occupants of such a place. Lucky for them, I guess.

:-)) Many years ago, I was nearing the end of a pop recording
which had gone on for several months. At one stage, when there
were a large number of soloists all arriving and departing at different
times of the day and night, the recording team slept at the studio to
be available as required. I did not go home for several weeks.

Then, a journalist from a well-known British magazine for ladies
telephoned our Technical Director and said that she would like to
write an article about record production. It was decided that
she should be assigned to my tender care. She turned up, mid
20s, pretty as a picture, bubbling over with enthusiasm, and said
to me: "Iain, I am so excited to be here. I have a million questions
for you, but the first thing I want to know is, how many albums
do you record in a day!"

Seems to me that, if they are being true musicians, they should be
expressing emotions. Assuming they are not just narcissistic, they must
have an audience in mind. I would want to quiz them on their sense of
other. Just who do they think they are playing for, and where do they
think they are. That kind of stuff.

Hmm.Interesting idea. I have hard classical conductors say that they
were "doing it for Sibelius" (or Mozart, or Rachmaninov) and there
is something in this, as they are bringing their interpretation of a work
to the public which otherwise might never be realised.

The physical and acoustic arrangements as you describe them are
interesting. Clearly each is sensitive to the sounds of others. That seems
a good start:)

It's a complex subject, but much more simple in the case of an
"acoustic" recording where say a classical orchestra is recording in
a concert hall.

But once to get onto multi-mic techniques, it starts to get a lot
more difficult. You must have separation and prevent leakage from
louder instruments onto other mics (drums onto woodwind mics
are a good example) So this means that the drummer sits in his
own box, and the various sections of the band (I use the term
band and not orchestra to make a distinction between this and
a classical session) are sectioned off by acoustic screens. This
now means that no-one can hear the drummer, neither can he
hear the rest of the band. So headphones need to be used to
provide a foldback signal. Each section of players, and
sometimes even each individual player may require something
different in a foldback mix. This is a very important factor
and something that needs the constant attention of the recording
engineer or 2E.

playing for me. More generally, do they see the studio as a means of
playing to an audience?

I am sure they do.
Most session musicians, including orchestral players are
so seasoned that they probably see it as "another session"
This is not to say that they do not make maximum effort
on every occasion.

It is interesting by the way, to notice the difference in the
type of people who make up a studio orchestra.
There are quite long intervals when the conductor is
rehearsing perhaps a single section of the ensemble,
that the others have to sit perfectly still and quiet, so many
bring a book or magazine to read. They often leave these behind,
and when clearing the studio you can quite accurately predict the
type of literature you will find in each seat. Woodwind players read
"The National Geographical Magazine" String players read "House
and Garden" while the ladies among them read "Vogue" or
"Cosmopolitan" Percussionists seem to read computer and motoring
mags, and brass players read "Penthouse":-)

Ask them, please. Are you playing for Ian?
They will think I am referring to myself:-)

PPS One objective of design should be to reduce as far as possible the
need for restriction of open-loop bandwidth.

What I really meant was gain at frequencies outside the audible band.

Many things were different, I have been told, including speakers and,
consequently, winding ratios, maybe. My opinion is that there are far
better transformers available now than then, in terms of materials at
least.

Yes indeed. Most speakers were 15 Ohms.
It is true that transformer materials are far better these days, but
there is a much smaller demand now, so price cutting is probably
common, which may adversely affect the production quality.

Back in the sixties, OPTs were cheaper than large high voltage
electrolytics.

Interesting to discuss these matters with you, Ian.

Cordially,

Iain Churches


.

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