Music Trade Review

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Wm.Braid White
Technical Editor
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JIIC
What Engineers and Physicists Are
Doing for the Development of Tone
*T HE current number of the magazine Radio
Engineering contains an article by John
Dunsheath describing a new instrument in-
vented by Arnold Lesti and Leo Tiedemann,
which makes use of the photo-electric principle
and which is intended to provide an universal
tone-producer of wide scope and virtually un-
limited variety. In these days, when the makers
of standard musical instruments are scanning
the skies of trade anxiously in the hope of
learning something of the future, it is highly
desirable that they should keep themselves in
touch with the work which is being done by
engineers ami physicists in this realm which
they have hitherto regarded as their own. The
audion tube has been responsible for a great
many amazing changes in social conditions. It
may some day be responsible for changes of
parallel import and violence in the realm of
musical art.
Musician vs. Scientist
It is highly necessary to remind my readers
that the work which is now being done in the
recording and reproduction of music is bound
to lead, sooner or later, to work in the field of
tone production.
Already engineers and
physicists, who in the early -days of electrical
phonograph recording and talking picture mak-
ing were willing to accept musical instruments
as they found them, are beginning to lay im-
pious fingers on these ancient and accepted
works. The musician and the scientist, un-
happily, live in worlds far apart from each
other. Neither can speak the language native
to the other. In this country, at least, very few
workers in science have more than a bowing ac-
quaintance with practical music. When such men
approach problems connected with the prac-
tical production of musical tone they come, of
course, unaffected by any ancient tradition, and
so have nothing to unlearn. On the other hand,
their approach is almost entirely theoretical and
in consequence they are always in danger of
evolving some fearful and wonderful piece of
apparatus which will fulfill the scientific require-
ments as well as it badly satisfies the needs of
the practical musician. Meanwhile, the musi-
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cians and the musical instrument makers remain
quite supine, apparently either ignorant of all
that is going on, or too paralyzed by fright to
have any power to deal with a situation which
daily becomes more threatening.
:
The Lesti Invention
I wish to discuss this situation; but first of
all let me say a few words about Mr. Lesti's
invention. In bare outline this consists of two
disks of glass placed side by side vertically and
parallel to each other, with their centers exactly
in line. One of these is stationary and the other
revolves. At one side of the rotating disk is
placed an electric light with a condensing lens,
and on the other side of the stationary disk is
a photo-electric cell. Suppose the lamp to be
shining and imagine a small transparent slit on
each of the two disks, all the rest of their sur-
faces being black. Obviously if the rotating
disk were rotated at the rate of, say, 600 r.p.m.,
the light behind it would pass through the
transparent slit and through the corresponding
slit on the stationary disk 600 times per minute,
or ten times per second. Thus, the photo-elec-
tric cell would receive ten light flickers (alter-
nations of light and darkness) per second.
There would, therefore, be set up in the circuit
of the iphoto-electric cell a current interrupted
ten times per second.
Suppose now, that instead of only one open
slit on the rotating disk corresponding with the
slit on the stationary disk there were, say,
forty-four, space.d evenly around the periphery
of the disk. If, then, the speed of rotation were
again 600 r.p.m., then obviously there would be
each second 440 light flickers through the sta-
tionary disk, and so an electric current in the
photo-electric cell circuit which would also
vibrate 440 times per second. Let this current
then be amplified and turned into the moving
coil of a loud speaker. Plainly the loud speaker
would give out the sound of the violin A, 440
vibrations per second.
Details
This in principle is the basis of the new
instrument. In detail it is, of course, consider-
ably more extensive. There are files of slits
on the stationary disk, running out radially
from the center. Each file contains slits of the
same shape and in number corresponding to at
least two octaves (twenty-four tones). The
Welte Mignon Experts
slits on the rotating disk are equal in number
of files and number to each file, so that for eacli
row on one disk, corresponding to a. given pitch,
is a row of slits on the other; Thus, as may
be seen, it is possible to obtain a note from the
keyboard of the instrument by pressing the key
and thereby opening a shutter, which permits
the light to shine through the corresponding
row of rotating slits and in turn through the
corresponding slit on the stationary disk.
Tone Qualities
This, however, is not all. As can readily be
seen, the scheme lefiTiS"'itself to variety of tone
quality. For if any giv«rf s $lk t>q-.the stationary
disk is cut to a .pattern corresponding with the
graphic wave-front shape of a given complex
sound, consisting of some set up of harmonics
with fundamental, the action of the slit in
passing across that shape will cause a light
flicker so spaced in its time pattern as to repro-
duce through the photo-electric cell a corre-
sponding vibration time pattern fti electric cur-
rents which will give corresponding-quality to
the sound which emerges from the loud speaker.
Now, when we realize that each of the slits
of the stationary disk is carefully cut to give
one wave length only in each case for each note
and that there is plenty of room for a large
number of files of slits, each file having its slits
cut to some predetermined Wave form, it is evi-
dent that this new instrument has possibilities,
if nothing more, in the way of tone production,
which assign it to the class of the large and
complicated concert organs now so much used.
I have given this description, which I hope is
clear, simply from my reading of the article in
Projection Engineering. The writer of this
article is not a master of the written word and
his descriptions are both complicated and ob-
scure. It is evident on the one hand that we
have here a very interesting and possibly sig-
nificant new achievement in the instrumental
means of music. It is equally possible that it
will remain an ingenious toy and nothing more.
It is certain that its inventor and its describer
alike have viewed their problem theoretically
and have overlooked a number of practical facts
which will make all the difference in the world
to the question of the instrument's being turned
to practical use. I shall say a word on these.
Theory and Practice
It is not difficult to work out formulas which
Thli
Label
Guarantees
Quality
PFRIEMER HAMMERS
Always Found in Pianos
of the Highest Quality
We install the original Welte-
Mignon Reproducing Actions
in all makes of pianos. Also
general renovating and re-
pairing of all types of player
actions.
Originators of the Re-enforced Tone
Producing Hammer
WELTE-MIGNON PIANO CORP.
Wales Aye. ft 142nd St., New York
Lytton Building, Cblearo
704 St. Ann's Ave.
25
-
New York
CHAS. PFRIEMER, INC.