Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to the synchronisation of ari unsprocketed
audio-tape, either having sound pre-recorded thereon, or intended to have
sound recorded thereon, which is to be absolutely in phase with the frames
on the motion picture film.
Prior art devices embrace spaced markings on the reverse (base)
side of the sound recording medium and the markings may be sensed reflec-
tively .
A substantial amount of prior art exists wherein a magnetic tape
is provided with synchronising information in the form of magnetically
recorded si~tnals. Such prior art i~ typified by the following: United States
Patents 2,475,439 (Waller et al), 3,047,675 (Berryhill), 3,650,609 (Lancor);
British Patent Specifications 1,139,402 (Yamada), 1,236,786, 1,236,787,
1,236,788, 123,789 (Bell and Howell) and Canadian Patent 617,139 (Cornell~.
A large number of systems for synchronising recording tape during
sound transfer operations are known. The more common synchronising
systems ar e known by thos e skilled in the art as Leeve r s - Rich , B . B . C .,
Nagra and Uher, *Pilot Tone, *Perfectone, *Telefunken, *Rangertone,
*Maihak and *Fairchild. All of these synchronising systems are intended
for u~e with magnetic tape and, with one exception, involve the placement
;20 of recorded synchronising signals on portions of the tape not utilised for -
the in'cended audio program material. Such portions may be adjacent the
edge of the tape or confined to the area adjacent the centre of the tape. The
aforementioned one exception resides in the *Fairchild system wherein
audio and synchronising ~ignals are superimposed. All of the above-
mentioned synchronising systems have pilot frequencies ranging between
50 Hz and 100 KHz. These 9y9tems are used mainly to synchronise the transfer
of information from unsprocketed strip to sprocketed strip.
The most serious disadvantages of the aforementioned prior art
will now be dis cu~ 8 ed .
Primarily, as with all devices relying upon generation of a
currentby the effect of magnetic flux change upon a transducer, the required
synchroni~ing signal cannot be generated until the tape is moving at a
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sufficient speed. Thus, only dynamic synchronisation is possible.
It is desirable that a synchronising system should be equally
effective for cueing tape recorded sound, for example, a radio program,
or indexing a film or strip having both audio and visual information, for
example, a television program although equally applicable to the production
of video tapes per se.
Light reflection systems are subject to interference by dirt etc.,
and are found unreliable.
Ithas been recognised by those skilled in the art that, a synchron-
ising system ~hould meet the following requiremer.ts:
1. Should compensate for uniform or non-uniform stretch of
of a magnetic recording tape due to ageing, changes in
temperature and humidity. (This stretch may give rise to
40 seconds error in 60 minutes of recording),
2. Should compensate for variations in mains frequency, ~-
3. Should be uninfluenced by slippage, wow and flutter,
4. Should not be susceptible to dirt or foreign matter on
the tape,
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5. Should have a relatively high resolving power,
6. Should compensate for tape capstan slippage, ;
7. Capable, if necessary, to indicate the direction of the tape
and/or the sign of the desired correction,
. Should not render the tape unsuitable for editorial markings
- and splicing notes which are normally applied to the tape
with wax pencil,
9. Should be reasonably mechanically robust, and
10. Most importantly, ~hould provide an error signal which is
related to true time or a speed reference dependent on media
in use, and not an arbitrary time based on tape or strip footage.
The present invention envisages meeting substantially all of the
foregoing desirable features.
In ce~cnce, thc invcntion illVOIVC3 thc deposition of at lea~t ol-e
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series of longitudinally spaced-apart areas of radio-acti~rity in-permoable
material on one surface side of a sound recording medium or other strip.
In use, a source of radio-active emission, alpha or beta particle, is placed
on one side of the recording medium and a suitable radio-active detector
placed on the opposite side of the recording medium.
Movement of the recording medium will then provide a succession
of pulses which may be fed into a comparator, which is also provided with a
second input which may be a standard frequency input signal or a signal
related to true time or a signal relative the speed of the visual or audio
media, thus producing an output error voltage which is a function of the
variation of transport speed of the recording medium related to the second
input.
In the playback or dubling mode, the pulse detected is fed into
a reversible counting system whichsould be tied to or related to a control ;~
system which would advance the tape, or reverse the tape, as required.
An important distinction between this invention and the prior
art ~sing areas of magnetised material having modulated signals thereon,
is that the output signal does not vary with linear speed, i.e. pulses willbe
produced, at full signal strength, immediately the film starts to move.
A description of the invention follows and should ~e read in
conjunction with the appended drawings, in which:
Figure 1 represent~ the basic inter connections between a tape
recorder and associated electronic components.
F-igures ZA to SA indicate various formats for disposition
of areas of radio-activity impermeable markings.
Figures 2B to SB indicate the approximate detector output s;gnals.
Referring now to Figure 1, there~ i~ shown a recording medium
1 which is transported, in the usual fashion, between a supply reel Z and
a take-up reel 4. Magnetic heads 6 and 8 associated with conventional
recording and/or playback form no part oE the present inve,~tion.
The tape 1 also passes between a source of alpha or beta
particle emission 10 and a suitable detector lZ. The reverse side of the
tape i9 imprinted with a series of longitudinally equally spaced areas of
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radio-activity impermeable material whose configuration will be discussed
with reference to Figures 2A to 5A and Figures 2B to 51~. At this juncture
it i8 ~ufficient to state that when the recording medium i9 being transported
the detector 12 provides a series of pulses of selected waveform. The
pulses pass to a multiplier where the frequency of the pulses is raised to
a value, for example 9600 Hz, which is adequate for use in a comparator
16. The comparator 16 i9 also provided with an accurate standard frequency
commensurate with the previously mentioned value, for example, of 9600
Hz. The comparator may be arranged to provide an output signal V which
0 i9 zero or maximum when the recording medium i9 moving at a synchronous
~peed. If the record medium lags behind or leads in front of the desired
nominal speed, the output speed is changed by the output voltage to effect
a correction to speed of the motor.
Figures 2A to 5A indicate different forms of marking for tapes.
Figure 2A shows a simple "ladder" configuration formed of a series of
equally spaced areas 20 along the length of the tape. Such a configuration
requires a single source 20 and a single detector 12 and will result in a
detector output consisting of a series of pulses as indicated in Figure 2B.
Such an arrangement will not indicate the direction of the tape relative
to the detector.
Fi~ures 3A to 5A indicate forms of marking all of which will
provide an indication of direction of tape as well as the degree of synchroni-
sation. The embodiment shown in Figures 3A and 3B has staggered areas
~; 22 and require the use of a second detector 12' (not shown) and possibly
a 3econd source 10' (not 9hown). The output 9ignal9 12 and 12~ produced
in the Figure 3A are shown in Figure 3B. In the Figures 4A and 4B
embodiment the areas are inclined and such inclination does pro~ide, if
necessar~, more space for the sources and detectors.
Figures 5A and 5B are directed to an embodiment wherein the
areas areOftriangular shape whereby the waveform generated by the detector
12 is indicative of the direction of the tape.
Since it i6 prinlarily the purpos e of us ing areas, other than simple
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parallel bands, to produce detector output ~ignals which are indicative of
the direction of movernent of the tape or film, other geometric configurations,
such as parallelograms, trapezoids, odd-sided polygons and possibly
semi-elliptical configurations could be used. Needless to say, the shapes
chosen should not have excessive dimensions in the longitudinal direction
otherwise the resolution attainable will be compromised.
In all the embodiments envisaged the areas are formed of a
radio-activity impermeable material~ such as, for example, barium sulphate.
In Figures 2A to 4A the areas comprise 1/16 inch stripe~ spaced l/8 inch
apart which, for a tape speed of 7 l/2 inches per- second gives an output
of 60 pulses per second. The ~ource may be any suitable alpha or beta
particle emitter such as Poloniwl 210 or Americium 241.
It will be appreciated that while the invention has been generally
described with reference to standard l/4" recording tape, the same techni-
que and apparatus may be used with any ~trip-like medium including
cinematograph film and the wider video tape~. It has been found that
material imprinted in accordance with this invention, may be subsequently ~ -
marked with editorial notes, timing and cucing marks all o which are
usually made with a wax pencil.
The output signals from the detector~ can be used not only to
effect synchror~isation of the recording medium but may be utilised in
computer controlled programming. The invention ha~ further application
when applied to cinematograph film which upon occasions, particularly
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~ ~ during editing, may need to be rever~ed in the direction of transportation.
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The ~y~tom leaves plenty of space on tape~ or films for the addition of
other information. The preferred marking material, i.e~ barium sulfate,
is rolatively inexpensive and easy to apply .
Other embodiments falling within the terms of the appended
claim~ will occur to those skilled in the art.
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