US2342395A - Control system for sound films - Google Patents

Description

Feb. 22, 1944. J. G. FRAYNE CONTROL SYSTEM FOR SOUND FILMS Filed Oct. 22, 1941 m n M 8 R llml m a C m ,6 m E a m P A '53 4 5 3 mm m F M I 5U HM mw a VA 2 3 C 8 9 E fl 2 m. M N fin V. L EDT w L m A m mw 7 N R 6 w p. 2 l

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UNITED STATES PATENT-OFFICE CONTROL SYSTEDIFOR SOUND FILMS John G. Frayne, Pasadena, CaliL, assignor to Western Electric Company,

poration of New York Application October 22, 1941, Serial No. 416,089

3 Claims.

This invention relates to sound recording systems and more particularly to systems for expandin he volume range of sound records photographically impressed on films.

It is the object of this'invention to provide apparatus andmethods by means of which sound picture films capable of reproduction in standard theatre equipment may be reproduced with greatly enhanced volume range in theatres which have been modified by adding to the standard existing apparatus a small amount of simple equipment. V I V A feature of the invention is the usetwith a sound picture film in which the picture and sound track appear in their normal positions and are or normal dimensions, of a control track of extremely narrow width. Owing to the extremely narrow width of the control track it may be placed between the sound track area and the picture area without interference with or from either area.

A further'feature or the invention resides in the provision of apparatus suitable for reproducing the soundtrack and associated control track after they have been simultaneously scanned by existing standard reproducing ehuipment. The invention will be best understood from the following detailed description, referenc be-' ing made to the accompanying drawing.

In the drawing: Fig. '1 shows the relative positions of soun track area. control track area and picture area on an enlarged portion of a standard motion Fig. 2 shows the auxiliary equipment necessary to utilize the sound recordand associated control trackofFig.1:and,

. Fig. 3 is a diagram showing the interrelation 01' various circuits used in recording the sound track and control record.

It is to be noted that that part or the equip ment which is used as monitoring equipment during the recording operation isidentical with the equipment used in the theatre during reproduction. 1

Referring now to Fig. 1 a portion or a standard photographic him is portrayed. Thefilm is provided with the usual sprocket holes 2. Picture areasoi' standard dimensions are indicated at I and a standard sound track or standard width The track shown is of the variable density type but may be any one or the relatively large number of types of sound tracks which are available at the present time. The control track is indicated Incorporated, a corat 5. This track is or extremely narrow width, being of the order of 5 mils in width. It is a record of varying frequency, the frequency range extending preferably from 2,000 to 4,000 cycles. A rectangle 6 indicates the manner in which a single scanning light beam may be used to scan both tracks.

Fig. 2 shows the invention "applied to standard reproducin equipment of the type more completely disclosed in U. S. Patent 094,063 which issued toJ. C. Davidson on September 28, 1937. It will be obvious that the invention may be practiced with any desired form oi film reproducing device.

A main housing 1 encloses a film driven roller 8 which forms a support tor the sound film at the translation point. A scanning beam passes through an edge portion of the film including the sound track and control track, to an optical system terminating in an objective lens {which projects an enlarged image of the records to a Film profixed slit in the back of plate l0. polling means and the optical equipment by means of which light from.an exciting lamp is projected for the so-called rear scanning of the film have not been disclosed in detail as they are disclosed in complete form in the above-mentioned patent to Davidson A beam splitting device of any well-known iform maybeused to divert that portion of the scanning beam which has traversed the sound track from that portion oi the scanning beam which has passed through the control track. This device is indicated by optical elements I l and I! mounted on the front face or the element on the rear 01 which the slit plate is mounted. The diverging beams are reflected by a mirror II to photocells l4 and II.

In practice it will probably be desirable to replace the standard slit plate M with a plate cartying a slit of slightly wider than standard dimensions, with the beam-splitting elements II and I2 previously mounted on the front or the plate, the whole constituting an easily mounted replacement unit.

. In Fig. 3 the outputs of rerecorders l6 and I1,

suitably mixed by means 01 control elements II ance with standard practice are supplied. The

mixed outputs of the rerecorders may be monitored by means of a monitoring loud-speaker l1 over path including a power amplifier ill and the upper contacts of a key 33. Sound track.

is recorded on the sound film by means of a light valve 29 and control track ii is recorded by means of a light valve to. Details of the film driving mechanism and of the light valves are not necessary to an'understanding or" the inven tion as they may be or" any desired form. Preferably the light valves 29 and 3t arepart of a unitary structure four-ribbon light valve such as has been standardln this art for some time.

in usin a iour ibbon light valve the only modification necessary is suitable masking of the pole pieces of the second valve so as to lay down the very narrow control track, which as has been previously stated, is of the order of 5 mils in width.

The mixed output of the rerecorders is amplifled in an amplifier 22 and supplied to the signal light valve 29 by means of a transformer LA noise reduction channel indicated generally at is bridged across the input to the signal recording circuit in accordance with well-established. principles which need not he discussed in this connecticu. The'output of the noise reduction unit which is rectified, and filtered current corresponcl irlg in'aniplitude to the envelope volume variations or" the sound is supplied to the light valve pacitor or inductor depending on the typ oscillator used, The output of the oscillator is subiect to volume regulation by means of a control element 25 and. supplies the control light valve til through a transformer ill. A portion of th varying light beam recorded on the film by light valves 29 and 30 is directed to monitoring photoelectric cells 32 and 33. The output of the signal cell 32 is amplified in an amplifier 34 and after further amplification is directed to loud-speaker M by way of the lower contacts of key 38. The output of amplifier 34 is subject to control by regulator which may vary either the volume or quality of the output. The output of cell 33' is applied to a discriminating network, so designed that the ratio of output voltage to input voltage varies with the frequency of the input in accordance with a suitable characteristic. The output of the discriminating network is amplified, rectified and filtered to provide a control voltage which is supplied to the variable gain amplifier 34 to regulate its volume. v

It has not been considered necessary to disclose specific circuits for the circuitelements dis- From the foregoing is obvious'that :2. him has been provided which is capableoi reproduction by means of standard theatre equipment in which case no use isinade oi the control track. when the theatre is to be equipped to obtain an enhanced effect it is merely necessary to add the auxiliary apparatus of 2, a variable gain urnplifier corresponding to amplifier and a discriminatortfi and its associated amplifienrecti fier and filter. l 4

' The use of a frequency varied control track has numerous advantages over th use of an ampli tude modulated control track, particularly when a track of very narrow width is contemplated. The-amount of expansion controlled by it is not subject to variations caused by fluctuations in sound track density, reproducing lamp intensity I or photocell sensitivity. it is also subject to much cussedin connection with Fig. 3. These circuit responding to amplifier 34'and photocell l5 sup plies a discriminating network corresponding to discriminator 35 which exercises a suitable control on the amplifier corresponding to amplifier 35. From this point the standard theatre power amplifiers and speakers may be used.

less variation due to accumulations of dirt and scratches which vary the transmissidn of the track.

While the signal to noise ratio of a 5 mil tract: is much lower than that etc. track of standard width, it has been found possible to obtain an ample range of volume control. in practice, the output of the control photoelectric cell is passed through a conventional filter, which passes ire quencies above 2000 cycles. The discriminator is tuned to @000 cycles. A 30 decibel range of volume control may be obtained.

Given a so decibel range of volume control may be desirable at times to utilize the system iorlncreasing signal-to-noise ratio rather than merely as an enhancing control. Thus a 2d deci bel range may be added to the upper V011 e level and the remaining 10 decibels utilized for bettering the signal-to-noise ratio of the film. if this is to be done, volume control must be operated to increase the level inthe signal channel supplying light valve 2% while simultaneously the oscillator control 39 is operated to produce a compensating adjustment on the control record. This method of operation produces a signal track in which the lower end of the volume range has been compressed and thus when reproduced in standard equipment will show a decreased overall volume range. When reproduced in theatre equipment provided with equipment utilizing the control track the slgnal-to-noise ratio is better,

clue to the fact that when thelower levels arewill be considerably improved.

Since the control track is intended foruse on the release print, it is recorded during thedub-= bing operation on the release negative. Various individual tracks are mixed in the usual manner to maintain the proper balancebetween music, dialogue and sound efiects. The control of the variable frequency oscillator ispreferably located in the mixing console.

- Whatis claimed is: c 1. In a sound film system, a sound picture fil including a normal sound track area, a sound track therein, a normal picture area, and a frequency-modulated control track of dimensions such that said control track may occupy the area between said normal sound track area and said picture area, and means for reproducing said sound picture film including a scanning device common to said sound track and said control track.

2. In sound 1 a. a picture film said reproduction, to volume enhancement under the influence of said control track.

3. In a sound film system, a sound picture film including a standard sound track area, a standard sound track therein, a standard picture area and a frequency-modulated control track 01 the order of 5 mils in widthoccupying the area between said standard sound track area and said picture area. a first standard sound-picture film projector, a second standard sound-picture film projector including a scanning device common to said sound track and said control track, said second projector being modified to include a plurality of photosensitive devices and optical means located between said scanning device and said photosensitive devices for operatively associating a photosensitive device with each of said tracks, means to project said sound picture film at times by means of said first projector, said standard sound track being reproduced without interference from said control track, and means to project said sound picture film at other times by means oi said second projector, in which case said standard sound track is subject, during reproduction, to volume enhancement under the influence of said control track JOHN G. FRAYNE.

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