Evening star., 1937-05-04
NEW RECORDING
PROCESS SHOWN
magnetic" Method Will
Make Single Record
Lasting Forever.
BY THOMAS r. HENRY,

A Cinderella step-sister Of the
epochal inventions Of nearly . half
century ago, which gave rise TO the
phonograph and later the sound NOV
ing picture, rose from her long OBJ
scurity in demonstrations before the
Acoustical Society of America meeting
at the Bureau Of Standards today.
This is magnetic recording" II
was first practiced by Danish college
professor in 1900 and then allowed
to lapse until its possibilities were
explored by the Bell Telephone Lab
oratories.
The method, as now improved, has
certain extraordinary advantages, it
was explained by DR.. c. N Hickman
Of the Bell Laboratories. 1t will make
a single record which will last forever.
Conversely, the sound may be COM
pletely erased and a new record made
on the same tape as often as one
pleases Its reproduction is remark
ably clear and its special uses are
expected to be in the study and the
business Office.
AWO A'ACtHVuSs
There are two primary methods Of
sound recording now in use Dr. Hick-
man explained. First is that in which
a groove is cut on wax or plastic
disk which varies with the modula-
tons Of the voice. There may be
either lateral or up-and-down varia-
tions in the ditch" in the wax and
these govern the movements Of the
diaphragm of the loud speaker In
reproducing the sounds. In electrical
recording they cause tiny currents
which are amplified and transformed
into sound.
Much Of the same principle is used
in sound pictures. except that the
modulations are those Of light and
dark shading on celluloid flm. These
light variations actuate tiny currents
which are translated into words and
music by the appropriate mechanisms.
The revived method Of recording IS
by an entirely different principle. BY
a complex process, modulations in the
voice cause variations in the mag
netic f1ux or variation in steel tape
or wire. Within the steel, literally
millions Of tiny magnets are made
with varying fields of force. Then,
when the wire is again passed under
magnet, the original sound is pro-
duced. The variations in the magnetic
field Of force can be used to set up
| tiny currents which can be ampli-
| fed to produce the sounds issuing from
loud speaker.
Field Lasts Forever.
Now a magnetic field, once set up,
lasts forever unless something is done
about 1t. A song or a speech thus re.
| corded is on record forever There
is nothing whatsoever to wear out.
The same result is obtained with other
types Of recording by making master
records which are kept in storage and
from which other records can be cut.
But the magnetism. and hence
everything that has been recorded,
can be completely erased instantly by
a simple process similar to that used
to demagnetize watches by jewelers.
This is of particular advantage. il
was explained, for dictaphone where
the same tape could be run through
again and again until 1t wore out.
After each use it would be de-nlag.
nified and emerge as good as new.
The original Danish experiments
were carried out simply with piece
Of wire. One Of the great improve.
ments introduced is the use OF a
steel tape two one-thousandths OF an
inch thick and so one-thousandthS
Of an inch wide Great Improvements
were also introduced in the system
of recording.
Symposium of Vibrations.
The specialists in the physics Of
sound devoted their session today to
symposium of vibrations, which are
closely akin to sound Among the
studies reported was that Of the
vibrations set up in a school building
by pupils exercising in the gymnasium.
1t was found that the rhythmic
movements of the exercisers set up q
vibration close to the natural fire.
quency Of the girder system This
brings to the front another peril to
be avoided by school building archi-
tects, since disturbance Of the girders
might seriously unbalance the struc-
ture Of the building itself.