I 151E
Sept. 8, 1959
J. v. ELLISON
2,903,521
BAND EXPANSION RECORDER
Filed Sept. 12, 1955
CONSTANT
TORQUE
SOURCE
an(“-M
ADJUSTABLE
SPEED SOURCE
10/
’
ADJUSTABLE
SPEED SOURCE
I 151E
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IlllIlllllIlllllllllllllllllllllllllllllll
INVENTOR
JOHN
BY
,
v. ELLISON
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Y
'f
M
.
ATTORNEYJ
United States } Patent 0
1
"ice j
2,903,521
Patented Sept. 8, 1959
2
.
j.
Yet another object of the present invention is to asso?'
ciate a recording means with a record medium‘ to put-
duce an effective recording speed which is different that!‘
2,903,521
the speed of the record medium.
.
.
A ?nal object of the present invention is to enable any:
BAND EXPANSION RECORDER
one torotate the recording heads associated with a play:
back means of a record/playbackrdevice to produce a
John V. Ellison, Washington, D.C.
desired frequency multiplication of the recorded signal.
Other and more speci?c objects of this invention will»
10 become apparentupon a careful consideration of the fol=
lowing detailed description when taken together with they
Application September '12, 1955', Serial No. 533,926
_ 2 Claims. (Cl. 179--‘100.2)
(Granted under Title 35, US. Code (1952), see. 266)
accompanying drawings, in which;
,_
V,
_ Fig. lcis a simpli?ed sketch illustrating the‘ recording
device and the relationship of the magnetic record me
The invention described herein maybe manufactured
and used by or for the Government of the United States
15
dium to the rotatable recording and playbackheads,
Fig. 2 is a section of the record strip illustrating the‘
of America for governmental purposes without the pay
magnetic track produced by separate recording heads on
ment of any royalties thereon or therefor.
the‘krotating record head assembly, and
'
_
. ‘
Fig. 3 is a perspective view of one playback head illuse
The present invention relates to a record/playback
device and more particular to a frequency band-expansion 20 trating the relationship of the head width and the double
track record medium.
I
recorder having an assemblage of rotating recording
Referring now to the drawings there is illustrated a
heads and an assemblage of rotating playback heads.
record/playback device comprising a magnetic record
A band-expansion recorder is a device which accepts
medium 10 adapted to be fed from a reel 11 which is
signals represented by a band of frequencies, records
these signals, and reproduces them at an accelerated rate. 25 equipped With a friction brake in order to maintain
proper tension on the magnetic record medium. The
By the process of acceleration, the signal frequencies are
record medium is fed from the reel 11 around an idler
all increased by a common multiplying factor, resulting
wheel 14 which acts as a guide, then through a metering
in an expanded band of Signal frequencies at the output.
device 12 which is adapted to be driven by an adjustable
In the present invention, advantage is taken of the redun
dancy present in the signal information‘ to be processed. 30 after
speedthe
source.
playback
Theassembly
meteringif device
desired.could
From
be the
p'ositi
meter‘
By means of multiple recording and playback heads
mounted in rotating assemblies, the signals are repeatedly
scanned at a relatively rapid rate to permit preservation
ing device the _ record medium is mevably mounted
of the timing during the band-expansion process.
to be driven at a peripheral speed which is less than‘ the
7
around a rotatable recording head assembly 15 adapted
In the prior art of record/playback devices, rotating 35 rate of the record medium, the record mediurn- is then
playback heads have been used but there exists a prob
lem of reducing wow and ?utter due to variations in the
threaded around a rotatable playback assembly 16 which
has an adjustable speed source and adapted to be driven
speed of the record medium during recording, playback,
at a peripheral speed greater than the rate of travel of
the record medium. From the playback head assembly
The present invention makes use of rotating recording 40 the record medium isv positioned around a second idler
guide wheel 17 and then is ?nally threaded onto a storage
heads whereby the relative effective recording speed be
or both.
-
tween the recording head assembly and a magnetic re
cord medium is such that the record medium can be
I reel 13 which is adapted to be driven by a constant
torque source to maintain proper tension on the record
medium. It is obvious that other guides could be posi
moved fast enough during recording and playback to
reduce wow and ?utter by means of speed stabilization 45 tioned along the record medium track wherever needed
Without departing from the invention.
techniques Well known in the art. Wow and ?utter are
The rotatable recording head assembly 15 as well. as
undesired’ characteristics found in recording and play
the rotatable playback head assembly 16 is formed of. any
back devices which are caused by irregularities in the
well known magnetic head structure mounted along the
speed of the record medium. They are nearly synony
mous terms, the distinction being that wow is the signal 50 circumference of a wheel having a rim made of a mate
rial with a low coefficient of friction which may be a
frequency deviation resulting from non-uniform motion
plastic or a non-ferrous metal, non-ferrous metal being
of the record medium recurring at relatively low‘ rates‘,
preferred.
7
while ?utter is the corresponding deviation resulting from
The rotatable recording head assembly 15 for illustra
non-uniform motion which occurs at relatively high rates.
tive purposes comprises four recording heads 21, 22, '25
In order to reduce these undesired characteristics both
and 24, the heads are shown as electromagnetic devices
the recording heads and the record medium are moved
having cores with short air gaps or slots- across which
at relatively high, though different speeds to permit the
the magnetic record strip travels. The signals are re
effective use of ?ywheels and other speed stabilizing
corded perpendicular to the edges of the record strip, that
devices on both the recording head assembly and the
is, across the record strip. The heads are equally spaced
record medium while maintaining a relatively low e?ec
90° apart along the surface of the recording head assem
tive recording speed equal to the difference between the
bly such that alternate recording heads are offset to form.
speeds of the recording heads and the record medium.
pairs that record on separate,’ parallel tracks thereby sue
It is an object of this invention to reduce wow and
flutter during recording and playback-on a magnetic
cessive recording heads record at the same time but on
record medium.
separate tracks as illustrated in Fig. 2. During record—
'
Another object of the present invention is to expand
uniformly a band of frequencies while preserving ampli
65 ing, the record medium travels over and contacts one
' half of the peripheral surface of the recording head as
ser‘rrbly and travels at a greater rate then the‘peripher‘a'l
speed of the recording head assembly, one head starts‘
A- still further object of the present invention isto em 70 recording on contact with the record medium and since
the record medium is moving faster than the peripheral.
prey an assemblage of rotating recording heads as a
v speed of the recording head assembly there will'be-s-lip-s
recording means.
tude information without compressing time duration of
signals occurring Within the accepted frequency band.
2,903,521
3
4
page between the record medium and the recording head
assembly. The slippage during 1A of a revolution of
the recording head assembly is such that the point of
contact of the next successive recording head with the
number of heads that contact the record medium per
sec., is used to determine the peripheral speed of the
recording head assembly for any number of recording
heads.
When the record medium contacts 50% of the periph
record medium will be at the point on the record medium
where the preceding recording head will break contact
with the record medium during the next 1%; revolution
eral surface of the recording head assembly a change in
the number of pairs of recording heads requires a change
of the recording head assembly. When the recording
heads are positioned alternately to record on separate
tracks the recorded signal will appear as shown in Fig.
2 wherein the last half of the recorded signal from the
preceding head is the same as the ?rst half of the signal
recorded by the succeeding head. All heads are con
nected with the same, common signal receiving source;
therefore, at anytime the heads are contacting the record 15
medium they will record the same signals.
,
_ Since the heads are positioned along the periphery of
the recording head assembly at 90° intervals and the
record medium contacts one half the peripheral surface
of the recording head assembly, as soon as one head
contacts the record medium and travels through one quar~
ter of a revolution the next successive head contacts
in the peripheral speed of the recording head assem
bly to prevent redundancy. When the difference in the
speeds between the record medium and the recording
head assembly remains constant with a change in the
number of heads then a change in the time per revolution
that a recording head contacts the record medium must
be changed. .
.
As illustrated in Fig. l, the record medium contacts
50% of the peripheral surface of the recording head as
sembly. At one r.p.s., the recording heads record on
- the record medium for one half second. When the
record medium contacts 50% of the peripheral surface
20 of the recording head assembly the number of heads must
be in pairs and by varying the number of pairs of heads,
the speed of the record medium must be changed.
In an alternative manner of recording, the speed of
the record medium, and during the next quarter revolu—
tion of the recording head assembly and movement of the
the record medium and the speed of the recording head
record medium over the recording head assembly the 25 assembly may be kept at the same speeds while the
two heads contacting the record medium will record the
number of recording heads is changed. In this case in
same incoming signal. This positions the assembly such
order to prevent signal redundancy the time (t) that
that the ?rst contacting head is ready to break contact
any one recording head contacts the record medium
during one revolution must be changed. Since the speeds
with the record medium, the second head has moved
through a quarter revolution and the third successive 30 remain constant and the time of contact changes, the
head is positioned to make contact with the record me
point that the record medium breaks contact with the
dium as the ?rst head breaks contact. This is a con
recording head assembly must be changed for different
tinuous operation, the two recording heads that are con
number of heads to obtain the proper recording angle.
tacting the record medium record the same signal when
Where the peripheral speed of the recording head as
in contact such that the last half of the recorded signal 35 sembly S,- is one revolution per second, the peripheral
of the preceding head is the same as the ?rst half of the
speed in inches per sec. will then numerically equal the
recorded signal of the succeeding head. The preceding
circumference of the recording head assembly, from this,
head during any recording period being the one in con
the radius of the recording head assembly can be deter
tact with the record medium during the time interval for
mined by the formula C=21rr. Also, as the recording
one quarter of a revolution of the recording head assem
bly that occurs just before the said recording head breaks
contact with the record medium, and the succeeding head
‘being the one that is contacting the record medium dur
ing one quarter revolution of the record assembly from
the moment of ?rst contacting the record medium.
It is not necessary that alternate recording heads be
positioned to record on separate tracks since it is obvious
40 head assembly makes one revolution per sec. and this
speed in inches per sec. is numerically equal to the cir
cumference, the point at which any record head must
break contact with the record medium when the speeds
are constant can be determined by the formula, d=tS,,
where d=the distance along the peripheral surface of the
recording head assembly that a recording head contacts
the record medium during one revolution of the record
ing head assembly, t=the time any one head contacts
the record medium during one revolution of the record~
that they can record on one continuous track, also, the
invention is not limited to one or two tracks but can be
used with as many tracks and as many rows of record
ing head assembly, and S,- the peripheral speed equals
50
ing and playback heads as desired.
numerically the circumference of the recording head
Since the record strip travels at a faster rate than the
assembly.
recording assembly it is obvious that there will be slip
In the illustrated example, the speed of the record
page between the recording head assembly and the
medium is taken at 7.5 in./ sec. and there are four record
record medium. The difference in the distances covered
ing heads along the periphery of the recording head as
over a period of half the time of a revolution of the 55 sembly. Since the record medium contacts 50% of the
recording head assembly being the effective recorded
periphery of the record medium and the recording head
distance along the record strip by each individual head.
assembly has a speed of one revolution per second, any
In order to get band-expansion, it is necessary to record
recording head will contact the tape for one half second;
the signals continuously without any overlap to prevent
therefore, the time t=1/2 sec. Substituting the values
redundancy. This depends upon the speed of the record 60 into the formula
medium, the peripheral speed of the recording head as
sembly, the number of recording heads and the time that
each recording head contacts the record medium during
one revolution. The speed of the record medium can be
any of the well known speeds such as 7.5 in./sec., l5 65
in./sec., 30 in./sec., etc. The formula
war-805%‘
where t=time that any recording head during one revolu
tion of the recording head assembly contacts the record
medium, St=speed of the record medium in inches per
sec., S,=the peripheral speed of the recording head as
sembly in inches per sec. for each revolution and N=the
70
S, see.=7.5 in.—3.75 in.
S, seo.=3.75 in./seo.
therefore, the speed of the recording head assembly must
be 3.75 in./sec. Since the recording head assembly makes
one revolution per second the speed in inches per sec
75 ond will equal to the distance a point on the periphery
cm
2,903,521
5
cores with short air gaps or slots across which the magnetic
record medium travels, for the playback heads the width
bly can be ascertained.
It has been found if the number of recording heads
are two, then the recording head assembly would be driven
at a speed which is exactly twice that of the record medium
in order to have a continuous recording.
6
In the operation of the device the recording heads and
the playback heads are electromagnetic devices having
travels in one second, this distance is equal to the cir
cumference of the recording head assembly. From the
formula C=21rr the radius of the recording head assem
of each head is wide enough to cover both tracks recorded
by the recording heads. The recording head assembly
rotates as the record medium moves over the heads but
the peripheral speed of the recording head assembly is less
than the record medium; therefore, the signal being re
In this ex
ample the same signal would not be repeated at any
time along the record medium but it is not necessary to 10 corded will be recorded along that portion of the record
medium which is the difference in the distance traveled
have a repeated recorded signal. When the signals are
between the periphery of the recording head assembly and
repeated during recording the speed of the playback head
assembly will be less during playback.
the record medium during contact.
The record medium travels from the recording head as
In a record/playback device wherein the number of
recording heads are two or more the ratio between the 15 sembly to the playback head assembly wherein the play—
back heads rotate at a peripheral speed which is greater
than the speed of the record medium. The playback heads
sweep the recorded signal a multiple number of times dur
ing an interval equal to a single recording interval where
speed of the record medium and the speed of the record
ing head assembly can remain the same and the formula
20
can be used to determine the time that a recording head
must contact the record medium to get a continuous and
repeated signal recording on the record medium. In order
to get a continuous signal with the last half of the signal
A1).
recorded by a preceding head to be the same as the ?rst
by the frequency band is multiplied according to the
peripheral speed of the playback head assembly and the
effective signal recording speed of the record medium
while the effective time duration of the signals remain
unchanged.
25
In the illustrated example of Fig. 1 the signals are
fed into all of the recording heads from a common
source and two of the recording heads are recording on
the record medium at all times but on alternate tracks.
half of the recorded signal from the immediately follow
ing head; either, the time that the record medium contacts
the recording head assembly, or the speed of the record
As shown, recording heads 21 and 22 are recording the
ing head assembly must be changed, when there is a change
same signal and when recording head 22 breaks con
in the number of recording heads. If the time of contact 30 tact with the recording medium, the recording assembly
between the record medium and recording head assembly
will have rotated so that recording head 24 will make
is constant then the speed of the recording head assembly
contact at the same time. The signal recorded by each
must be changed. If the speed of the record medium
succeeding head on contacting the record medium for
and the recording head assembly remains constant with 35 the ?rst 1%; revolution of the recording head assembly
an increase or decrease of the number of heads, then
the time of contact between the record medium and re
after making contact will be the same as the signal
recorded by the preceding head during the second 1A
revolution of the recording head assembly; therefore,
cording head assembly must be changed.
In either case the above formula can be used to deter
mine either the speed of the recording head assembly or 40
the time that a recording head must contact the record
medium during one revolution of the recording head
assembly for any desired number of recording heads and
desired speed of the record medium.
any two heads are always recording the same signal but
on separate tracks. Since the signals recorded by each
successive head is the same for one half the recording
interval; each playback head sweeps the same signal a
multiple number of times while the recording medium is
contacting the playback head assembly.
In order ‘to playback the recorded signal at an acceler
The playback assembly can be rotated in either direc~
ated rate, a playback head assembly 16 which comprises 45 tion to have the same frequency multiplication factor.
playback heads 25 and 26 mounted 180° apart and having
The assembly must be rotated faster when rotated in
a head width wide enough to sweep the doubly recorded
the direction of the record medium than it is when rotated
signal tracks is used. This assembly is rotated at a greater
in a direction opposite that of the record medium.
speed than the magnetic record medium which is movably
For any frequency multiplication factor X, the follow
mounted around one half the peripheral surface thereof in 50
ing
formula,
order to accelerate the frequency of the signals recorded
SP :l: S:
on the magnetic medium. Since the last half of any one
X *s . - s.
recorded signal from one recording head is the same as
the ?rst half of the recorded signal from the immediately
succeeding head but on a different recorded track, the
~"HA
can be used to determine the unknown, where X=the
double track playback heads of the playback assembly
frequency multiplication factor; St=speed of the record
relationship of the effective recording speed, the peripheral
speed of the record medium and the peripheral speed of
metering device 12 at a speed of 7.5 inches per second
and the recording head assembly is rotated one revolution
medium; Sr=peripheral speed of the recording head as
sweep alternately the recorded signal of each recorded
sembly; and Sp=peripheral speed of the playback head
track. As the playback heads rotate, the signal of one
assembly. In the formula, if the playback assembly is
recorded track is picked up by a playback head and as
the playback head leaves the recorded signal on one track 60 rotated in the direction of the travel of the record medium
the speed of the record medium (8,) must be subtracted
the same signal is immediately picked up by sweeping
from the actual peripheral speed of the playback as
the recorded signal of the next adjacent magnetic track.
sembly (Sp) to get the effective playback speed. If
Since the playback heads are 180° apart, as soon as one
the playback assembly is rotated in a direction opposite
playback head breaks contact with the record medium the
other playback head makes contact and immediately starts 65 to the travel of the record medium, the speed of the
record medium (St) must be added to the peripheral speed
playing back the recorded signal. The playback heads,
of the playback assembly (Sp) to get the effective play
being of a type which sweeps the doubly recorded track,
back speed.
play back the recorded signals from one track and then
In a typical example, for a frequency multiplication
the other without a break and since the playback as
sembly has a peripheral speed which is greater than the 70 factor of twenty, in order to ?nd the actual speed of
the playback head assembly, the following speeds are
record medium, each signal will be reproduced over sev
noted. The record strip 10 is fed from reel 11 by the
eral times and the frequencies multiplied according to the
the playback head assembly.
75 per second.
The recording head assembly 15 has a
7
52,903,521
8
circumference of 3.75 inches; therefore, the peripheral
" Obviously many modi?cations and variations of the
speed is 3.75 inches per second making an effective
recording speed of 3.75 inches per second. Since the
present invention are possible in the light of the above
teaching. It is therefore, to be understood that within
the scope of the appended claims, the invention may
be practiced otherwise‘than as speci?cally described.
What is claimed is:
1. A record/playback device comprising a record
medium, a rotable recording head assembly with a plural
frequency multiplication factor of twenty is desired, and
if the rotation of the playback head assembly is in the
direction of the movement of the record medium, from
the formula
X:
SpiS,
it is seen that the peripheral speed of the record play
back assembly must be 82.5 inches per second.
10
If the
ity of recording heads thereon positioned along the pe~
ripheral ‘surface thereof, said recording heads being
equally spaced, alternately staggered and connected to
a common signal source thereof, and adapted to record at
least two record tracks on said record medium with one
rotation of the playback assembly is opposite to that
of the record medium, from the formula
half of each recorded portion of one track being the
15 same as the alternate recorded portion of the other track,
it is seen that the peripheral speed of the playback as
sembly must be 67.5 inches per second.
a rotatable playback assembly with a plurality of play
back heads thereon positioned along the peripheral sur
face thereof, each of said rotatable playback heads hav
ing sut?cient gap width to simultaneously scan and re—
The band-expansion technique may be applied in many 20 produce signals from both of said record tracks, means
situations where signals which exist in narrow-band form
for moving said record medium along a path in which
may be more conveniently processed by converting them
said record medium contacts a portion of the peripheral
to Wide-band signals. For example, the band-expansion
surface of said recording head assembly and said play
recorder may be used in conjunction with a wave analyzer
back head assembly, said record medium having a speed
to permit detailed analysis of the spectrum of a nar 25 greater than the peripheral speed of said recording head
row band of signals. The resolving power of the
assembly and in the same direction of travel, said speed
wave analyzer is increased by an amount equal to the
difference providing an effective recording speed which
band-expansion factor. An extension of the lower fre
is less than the speed of said record medium which re
quency limit of a wave analyzer or similar measuring
duces wow and ?utter during recording signals on said
device is possible when the band-expansion recorder is 30 record medium.
used to shift the signals to be measured to a band
2. A record/playback device according to claim 1
within the frequency range of the instrument.
wherein the peripheral speed of said playback head as
Another application of the band-expansion recorder,
sembly is much greater than the speed of said record
in conjunction with electro-acoustic transducers and suit
medium.
able amplifying equipment, is to render audible sounds 35
which occur at frequencies below the range of human
References Cited in the ?le of this patent
hearing while maintaining in strict proportionality the
UNITED STATES PATENTS
relationship of all frequencies present in the signal. As
an example, the subaudible band from 6.4 cycles per
2,170,751
Gabrilovitch _________ __ Aug. 22, 1939
second to 12.8 cycles per second can be expanded by a 40
factor of 20 times to yield at the output of the expander
the audible frequency band from 128 cycles per second
to 256 cycles per second.
2,352,023
2,539,837
2,661,397
Schuller _____________ __ June 20, 1944
Howell _____________ __ Jan. 30, 1951
Berens et al. ________ __ Dec. 1, 1953
2,755,422
Livingston __________ __ July 17, 1956
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