Re: Ruben's tube

On Jul 27, 10:53 am, w...@xxxxxxxxxxxxxxxx (J. B. Wood) wrote:
In article
<43b4994f-e814-4be0-8082-7e93c84b3...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, LJS

<ljsche...@xxxxxxxxx> wrote:

 > Which  would display a composite of a wave form  created by inputting

the electrical signal of a musical pitch created by an instrument such
as a clarinet, captured by a microphone assuming that the raster is
tuned to keep the display steady and viewable?

LJS

Hello, and "waveform" generally refers to something varying w.r.t time.  I
tend to use the term "pitch" to refer to the fundamental frequency to
which the musical instrument is tuned.  The instrument's timbre of course
is determined by the presence of overtones/partials.

To capture the waveform of a musical instrument we would use a mic, audio
frequency amplifier (of sufficient bandwidth to include the relevant
partials of the instrument) and an oscilloscope connected to the amplifier
output.  The mic/amplifier should be of sufficient quality as to not
contribute significant artifacts to the waveform being measured. The
acoustics of the measurement environment (e.g. a small room vs. a concert
hall) will also contribute to the results.

I should add that with well-defined waveform shapes such as sine, square,
sawtooth, and triangular we get a good idea of the harmonic makeup of the
waveform.  This is much more difficult with a musical instrument owing to
the number of partials produced, their relative amplitudes and phases, and
the inharmonicity inherent im many acoustic musical instruments.  It's the
overtones/partials that cause the waveform to deviate from its
single-frequency sine wave shape.

OTOH, if what is sought is a display of an instrument's pitch and the
amplitudes of its partials, then a spectrum analyzer is appropriate.  

Just keep in mind that the time domain and frequency domain
representations are equivalent.  They're just different ways of expressing
the same phenomenon.  Kind of like using logarithms (cents) instead of
ratios or vice-versa to represent differences in pitch.  Depending on the
application it's often easier to work in one domain instead of the other.
Sincerely,

John Wood (Code 5550)        e-mail: w...@xxxxxxxxxxxxxxxx                    
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-533

Isn't that saying that if you want to look at the wave formed by the
composite of the overtones of an instrument that one would use an
oscilloscope? In this case the actual pitch is not really relevant..
One would be looking for the waveform of the "composite of the
overtones" that made up the sound. If one wanted to look at what are
the actual overtones and components that produced this composite, one
would then have to "analyze" the individual components and amplitude
of the various elements of the "spectrum" that produced this
"composite". Then one could then display the "composite" that is seen
in on the oscilloscope.

As I tried to explain, one could see the "composite" of the wave and
its overtones of a musical instrument on an oscilloscope. The other
part of my statement then said that the Ruben's tube should indeed
produce this same composite if it had higher resolution as in the
description, the video presenter mentioned that it was the compression
wave and its strong and weak points that produced different pressure
to show the wave as it affected the gas in the tube. Since the wave of
a musical instrument would have this composite built into it, it seems
perfectly clear that resolution is the only different factor in this
particular aspect of the two instruments.

My surprise, however, was that there was a mechanical instrument that
would show any wave form in this manner. I was pleasantly surprised as
well to see the use of fluids to show the compression waves as one
generally assumes that the sine wave shape is somehow being
transmitted by sound through the air. As I understand it, it is not.
Compression waves moving through air are different than radio waves or
electrical waves. They have a lot in common, especially from a
practical use standpoint, but their nature is, as I understand it,
rather different.

Looking at radio waves, I see it this way. There are AM waves and FM
waves. AM of course is Amplitude Modulation and FM is Frequency
Modulation. The oscilloscope produces AM type of waves as it appears
on the scope. The FM waves are more like my idea of compression sound
waves. The back and forth motion of a speaker is a series of pulses
that change the air pressure quickly and produces a series of high and
low pressures as it moves through the air or other matter.

The usual visual of the waves are dropping a pebble into the water and
the ripples that occur are then cross sectioned and this is what we
think of as the WAVE FORM. I believe that both the Oscilloscope and
the Ruben's tube display this same principle They take the compression
wave and display it as a graph of the amplitude of the sound as it
receives it. In the oscilloscope, the actual conversion takes place
with the microphone. (on the other end, the electronic wave generated
by the microphone is then converted back to the compression wave by
the speaker in a sound system).

I have not fully considered all the factors of the Ruben's tube, but
it seems to do pretty much the same thing. the compression wave going
through the tube is converted into a display of amplitude caused by
the increase and decrease of pressure of the compression wave.

This was my comparison and it seems as though you have included
another way or two that the same result can be achieved. The
oscillograph would make a visual chart of the raw wave that goes into
the scope. The scope would produce a picture that is pretty much the
same if the raster rate is in tune to the frequency of the pitch being
produced, if there is no raster rate then the oscilloscope would only
show an undulating vertical line, but when stretched out, it would be
producing the same result of a oscillograph.

The Spectrum Analyzer is one that I have never owned and worked with
(maybe a little on the computer) but as I understand it, it may take
the various partials heard individually and show all the elements that
are inherent in the sound. How it does this is not something that I
have had the opportunity to explore first hand, but the result would
show exactly each partial and the amplitude of each and then you could
of course build the composite wave.

This is fine and true (I think, I do take your word for it.) and it is
also more information than I claimed for the oscilloscope as I only
pointed out that it would give one the composite. I did not claim that
it would give one information on what caused this composite. Of
course, an experienced person might see the stronger overtones in the
composite and recognize them, but this also is more than I claimed.

Thank you for the definitions and explanations. I would only ask, "How
does a Spectrum Analyzer isolate the overtones and see them as an
individual entity?" I can see how one can use the O-scope to tune the
tones of the whole number ratios to a series of wave generators and
they could then be combined with various levels of amplitude as you
combined them and then the desired waveform composite of a clarinet or
trumpet could be created, but the reverse, that of plugging in a
microphone and analyzing the composite to get the overtones that
produced them is the only mystery I have with these instruments.

LJS

.

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