US3872264A - Audio response device with orthogonal scan of multiple tracks on playback - Google Patents

Abstract

An audio response data storage system including a plurality of voice frequency range sound tracks of approximately one half second duration. The system employed uses an orthogonal scanning technique which obtains automatic multiplexing of all of the tracks for access over a very small period of time. Scanning speed is at approximately five times the real time readout rate, and the entire record is scanned in approximately one tenth of a second, whereby data from any selected track segment does not suffer more than a one tenth second cueing time delay, resulting in a complete absence of choppy timing and the obtaining of a good natural sounding speech when the device is used as a voice response generator.

Description

United States Patent 1 91 1111 3,872,264

Cotter Mar. 18, 1975 AUDIO RESPONSE DEVICE WITH 3,674,922 7/1972 Salaman l78/DIG. 3 3,701,846 10/1972 Zenzefilis l78/DIG.3 ORTHOGONAL SCAN OF MULTIPLE 3,769,468 10/1973 Shutterly 179/1003 A TRACKS ON PLAYBACK Mitchell A. Cotter, Riverdale, NY.

[73] Assignee: APM Corporation, Englewood, NJ.

[22] Filed: Nov. 1, 1972 [2]] App]. No.: 302,822

[75] Inventor:

Primary Examiner-Bernard Konick Assistant Examiner-Alan Faber Attorney, Agent, or Firm-Charles E. Temko [57] ABSTRACT An audio response data storage system including a plurality of voice frequency range sound tracks of ap- [52] 179/1003 179/1003 ig fii proximately one half second duration. The system em- {511 Int Cl Gllb 7/02 ployed uses an orthogonal scanning technique which ['58] Fie'ld A DIG q. obtains automatic multiplexing of all of the tracks for 79/100 "A"" 6 access over a very small period of time. Scanning speed is at approximately five times the real time readout rate, and the entire record is scanned in approxi- References uted mately one tenth of a second, whereby data from any UNITED STATES PATENTS selected track segment does not suffer more than a 2,644,857 7/1953 Pierre l79/l00.3 A one tenth second cueing time delay, resulting in 21 2,900,443 8/1959 Camras 179/1002 T complete absence of choppy timing and the btaining g fg of a good natural sounding speech when the device is 0 mar 3,383,462 /1968 Banning 179/1002 CR used as a response generator 3,585,293 6/1971 Crowder 178/67 A 3 Claims, 10 Drawing Figures 22 c127 POWER 'EQQI 2/ PULSE LINE fi AMPLIFIER SUPDLYA /6 f TQANSVERSAL g 30 FILTER PT 7 2t? sYNC TRACK g S EP COMPARATOR PULSE DR m (S BET) COUNTER OUT-OPRANGE i 1 1 3/ I t 1 "1 "1 1 1 PWM DISCDIMINATOR 4 1 e INTEGRATOR it TlMING CHAIN & l i 1 3 TRACK SELECT 1 8BIT+SIGN 1 REGISTERS A/D 1 37 1 'L' -22 l REAL TIME 1 1 CONVERTER l BASE r CONTROL LOGIC CLOCK yo COMPUTOQ 1 t2 1 1 EXTERNAL i COMMANDS PATENTEU MAR] 1 75 SHLU 2 UP 6 A52 CONTROL COMPUTED r i STEERING ADDRESS MULTIDLEXER 1 TO CHANNEL GATES M TRACK UNT T CO STA E SEOTOD COUNT STATE HHHH m S cOM PARATOR SECTOR H COM PADATOR SECTQF? SELECT TRACK SELECT COMMAND R EGISTER FATENTED 1 81975 3, 872.264

sum u ur g DATA OUT I 0f; 3r M AL BL $57 A READOUT A g DEALTIME CLOCK BSHIFT REG- w ASHIFT REG- DATA OUT ISTED SET ISTEIQ SET BDATA 'IN /Z? A BL A DATAIN LOAD CLOCK B A sYNcasECTom 54 L L 27 INHIBIT GATE C* BINDEX AINDEX A MEMORY C SUMMED DATA IN L CQNTQOL CONTROL J LOGIC DATA 8 BIT DATA IN +SIGN R A/D .g DIGITAL ADDEQ CIONVEIIZTER SYNC a SECTOQ'I I INHIBIT GATE mmEm- 1 8% 3.872264 sums or 6 E DGE D E LAY 4COUNT 64- COUNT RESET ALL X 3 BIT 6 BIT AUDIO RESPONSE DEVICE WITH ORTHOGONAL SCAN OFMULTIPLE TRACKS ON PLAYBACK This invention relates generally to the field of data storage, and more particularly to the storage and retrieval of syntactical and phonemic data for audible reproduction. Reference is made to my co-pending application, filed jointly with Bernard David Nadler, Ser.

No. 295,234, filed Oct. 5, 1972, now U.S Pat. No.

3,810,106, and entitled SYSTEM FOR STORING TONE PATTERNS FOR AUDIBLE RETRIEVAL,

which discloses and claims related inventions. The

present disclosure relates to a relatively simpler device particularly adapted for the reproduction of a stored spoken vocabulary.

BRIEF DESCRIPTION OF THE PRIOR ART In prior art devices, audible sounds are normally stored in parallel tracks upon rotating drums or other moving storage mediums, and a separate pick up or other retrieval device is used for each track. Given consideration of space and cost, most audible retrieval devices in the prior art are limited to relatively small vocabularies of the order of less than 50 words, and seldom exceeding 100 words.

In the above mentioned co-pending application, which is assigned to the same assignee as the instant application, there is disclosed a somewhat analogous system particularly suited for the storage and retrieval of musical tone patterns. The device includes a generally rectangularly-shaped storage record having a large plurality of recorded sound tracks of finite length arranged in parallel juxtaposed position upon the record. The record is scanned orthogonally at very high speed in raster-like fashion such that each deflection of scanning being prependicular to the axis of the sound tracks crosses all of the tracks, thus potentially reading all of the information contained in the record to make the same available for retrieval over a very short period of time. Scanning is performed using a laser beam, and electro-optical reproduction is performed at a far greater rate than real time output rates. Analog retrieval signals are converted to digital values, and are rapidly stored using one or more storage registers which are then unloaded at relatively slower intervals, the retrieved signals then being again converted to analog values, suitably modified, amplified, and transduced.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present disclosure relates to an analogous system which can be manufactured at substantially lower cost using substantially less sophisticated hardware, and is of value where the demands of the system are substantially less. In a speech retrieval device, normally a vocabulary of several hundred words is adequate, and if a greater vocabulary is required, it is possible to store the data in terms of phonemic and syntactical elements, rather than in entire words. Since normal speech proceeds at a far slower rate than musical reproduction, expensive items such as a laser beam scanner are not required, and pulse modulation parameters are well within the capability of simpler scanning equipment, such as cathode ray tubes and the like.

However, it is often desirable for a voice response system to have multiple outputs independent of each other in order to supply multiple responses with a single system. The present embodiment therefore includes timing and addressing means, including comparators which produce an output command for a sampling pulse to occur when the address in a register loaded by the control logic agrees with the status of the timing chain. This output command may be multiplexed to any number of samplers and related output circuits by yet another address delivered by the control logic. The control logic orders the called channels into a sequence in increasing order of channel position so that as the y scan progresses it may steer the channel or track data to the correct output by the address in the multiplexer. Each individual output requires its own sampler gates, as well as a signal demodulator, digitizer and real time converter. These elements may be, for the most part, inexpensive digital hardware, and they readily lend themselves to further integration to result in a very economic approach. The control timing logic is common to all the outputs, and need not be expanded to handle all of a hundred channel outputs or more.

The lowered cost of manufacture is principally the result of slower scan time as well as less data and storage of the same. While the current gates and digitizer are all able to operate at a faster speed than disclosed, scan speed is determined by these and another feature of the system. The choice of number of tracks and the length of the record together with the minimum sampling time determine the overall scan time. The number of data points multiplied by the minimum sample time equals the scan period. The minimum time in the disclosed system arises from the decay rate of the phosphor of the cathode ray tube scanner. The fastest currently available phosphor decay is found in a thin layer (about 1 mg/cm of P 16 type CaMgSio zCe activated and quenched to speed up decay. This phosphor emits principally in the ultraviolet range centered at 380 nm. with about 5 percent efficiency. For very rapid scanning, the decay which is of the order of 50 to nanoseconds for 1/e of output becomes a limitation on the discrimination between two distinct openings in the data record track. The attack time or build up of radiation is extremely fast, being less than a few nanoseconds. In order to enhance the detector response from the record, the tracks differ in configuration substantially from those of the above mentioned co-pending application. Each track has a sync or start gap in a periodic position, and the modulation occurs by moving the position of a second gap in relation to it. While the reference gaps are all in a periodic position in space on the record, the scan may not be that precise that the modulation gap could be used alone against a precisely clocked start pulse. Without a great precision in the deflection of the scanner, this could not provide the low noise and accurate modulation of the scanned sample light pulse position. The reference gap is used to control the deflection sweep by locking it to the clock system through position feedback by comparing the reference pulses with the clock. The light pulses are then able to operate a pulse width or position discriminator. Because of the slow decay of the phosphor, a transversal filter is used to differentiate the light output of the photodetector by providing pulses coincident with the rising edges of the gaps as represented by the sampling light pulses. The minimum gap spacing chosen (50 microns) represents for the scanning rates selected. a pulse to pulse time of only just under 10 nanoseconds. Without a transversal filter the system would not function, and with a practical version of the filter, the scan rate disclosed is approximately the maximum. The photodetector chosen does not contribute to the response speed limits, as it is so much faster and in this respect, the use of the filter is relatively different from that disclosed in the above mentioned application.

In order to obtain a sufficient number of photons into the photodetector at acceptably low electron beam currents, it is necessary to use a fiber optic cathode ray tube faceplate. High beam currents tend to burn the phosphor screen and limit operating life. Using a lightly alumiriized screen (about 100 nm) the fiber optic faceplate increases light output over that from solid faceplates by more than 20 times. The glass fibers are chosen for good near ultraviolet transmission, and are microns or smaller in diameter. To prevent scatter and loss of resolution and radiant energy level, the faceplate and the data record plate are mounted with an immersion oil fluid filling the glass to glass air gap. The oil has an index of refraction approximately the same as the glass faceplate and glass record. The collimated radiant energy from the fibers is therefore undivergent in its passage into and through the data record plate. Once through, the energy is collected by a lens and a photodetector system.

The modulation is of pulse width modulation type, and as compared with the disclosure in the above mentioned co-pending application, emitter coupled logic is adequate since the speed of tunnel diodes is unnecessary. The modulation pulse position moves plus or minus 75ns. for 100 percent modulation. The modulation provides 40 to 50 db of signal to noise ratio, and does not vary with the aging of the cathode ray tube or the word selection position. The noise is sensitive to scan rate changes, but the disclosed deflection feedback system serves to lock the sweep smoothly to the record tracks, and thereby to the timing chain. It is important in the disclosed system that the sweep not have any significant noise modulating its sweep speed across a single track (high frequency type) of from slice to slice and so on as the scan progresses down the track which would produce frequency noise. The locking action provides correction for both types of noise.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, to which reference will be made in the specification, similar reference characters have been employed to designate corresponding parts throughout the several views.

FIG. 1 is a schematic block diagram of an embodiment of the invention.

FIG. 2 is a schematic side elevational view of the cathode ray tube scanner interconnected to the data record plate forming a part of the embodiment.

FIG. 3 is a view in elevation of the data record plate.

FIG. 4 is a fragmentary enlarged view of the data record plate corresponding to the upper left hand portion of FIG. 3.

FIG. 5 is a much enlarged fragmentary view of the data record plate showing adjacent segments of two data tracks.

FIG. 6 is a schematic elevational view of the data record plate showing the progressive vertical scan.

FIG. 7 is a block diagram showing the operation of alternately stored and unloaded data output registers.

FIG. 8 is a block diagram showing Y scan clocking.

FIG. 9 is a block diagram showing X scan clocking.

FIG. 10 is a block diagram showing address means used in conjunction with multiple output channels.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT In accordance with the invention, the device, generally indicated by reference character 10, comprises broadly: (see FIG. 1) a control logic computer 11, serviced by an external command interface 12, and having a control link 13 to a timing chain and track select register module 14. The last mentioned module controls a sweep drive 15 controlling a power supply 16 and yoke 17 of a cathode ray tube scanner 18. The scanner 18 scans a data record plate 19 and interposed between it and a photo detector 20 and storing words or phenemes. The output of the detector 20 flows through a transversal filter 21 to a pulse line amplifier 22 feeding a data buss to be sampled 23 supplying auxiliary output systems 24, 25 and 26. The amplifier 22 also feeds a track pulse counter 27 feeding a sync comparator 28. A link 29 interconnects the comparator 28 to the sweep drive 15, and a second link 30 interconnects it to an out-of-range indicator 31. The timing chain module 14 includes a link 32 to a crystal controlled base clock having a base frequency of 9.398160 Megahertz. Another link 33 interconnects to a data AND gate 34, the output of which is fed to a pulse width modulation discriminator and integrator 35. The output of the integratoris to an 8 bit-plus-sign analog-to-digital convertor 36 in turn, feeding a link 37 to a real time convertor 38 having digital to analog output. This output is controlled by a link 39 to a low pass filter 40 and thence to an amplifier 41 and audio output 42.

The control logic computer 11 may be of conventional type, responding to one or more commands serially introduced, in response to which the computer unblanks selected portions of the data record plate 19 for the corresponding data. As will more fully appear hereinafter, the computer can service a plurality of demands, responding in the order in which the corresponding data is reached as part of a continuous scanning operation. The information can be gated to separate outputs as a result of an address command. A typical example, would be a telephone subscriber service for stock market quotations, in which the output of the system is interfaced to a telephone switchboard mechamsm.

The cathode ray tube scanning system 18 employs several known elements in a novel operative combination. The tube 48 includes a five inch square face formed by a ground fiber-optic faceplate 49 which serves to collimate the output of the scanning beam along an axis parallel to the principal axis of the tube. The faceplate 49 is surrounded by an oil seal 51 which entraps an immersion oil film 52 filling the interstice between the faceplate 49 and a surface of the data record plate 19. Energy emanating from the plate 19 passes through a focusing lens system 52 to fall upon a (5 1 than 3H2. Referring to FIGS. 3 to 6. inclusive. the data record plate 19 is in the form ofa 5 inch X 7 inch metalclad plate, microflat grade 2, 0.250 inches thick (Eastman Kodak Company). The metal-clad surface faces the scanner. It is bounded by an upper edge 57, a lower edge 58, and side edges 59 and 60. The recorded area 61 is 4.282 inches square and is divided into five sectors 62, 63, 64, 65 and 66. The first sector 62 is bounded by a start sync band 67 of width 0.06304 inches (64 X microns). Each sector is 0.806715 inches in width (819 X 25 microns). The sector sync bands 68, 69, 70, 71 and 72 are each 0.03152 inches (32 X 25 microns).

As best seen in FIGS. 4 and 5, the horizontally recorded tracks 73 are of a total width of 550 microns, including a micron clear band 74. The modulated portion of the track 75 is also 30 microns wide, so that the opaque metal film of the plate is open only in the 30 micron areas 74 and 75, for reasons which will become more fully apparent hereinafter.

Referring to FIG. 6, the scan pattern starts with an oversweep of the top edge 77 of the recorded area near the dot 78 and proceeds top to bottom, with the y sync proceeding from left to right. There are 819 scanning slices in each sector, with each sector sync ba'nd being 32 slices wide.

FIGS. 8 and 9 disclose the y sweep clocking and x sweep clocking, respectively. Pulses from t the base clock 80 pass through a two to one divider supplying pulses of 9.39816 Megahertz frequency to an AND gate 82 to a 4 bit counter 83, the output of which feeds an OR gate 84. The output of the gate 84 is fed to an AND gate 85 which gates the start of the y sweep and unblanking of the scanner. A link 86 feeds a link 87 to an AND gate 88 to an 8 bit counter 89 which counts the 200 horizontal tracks as they are orthogonally scanned. At the completion of each slice, a signal from an invertor 90 inhibits the gate 88, and the same signal starts the retrace for they sweep. This signal sets an AND gate 91 to a 4 bit counter 92 which counts the 8 intervals constituting the end sync period, the counter then resetting the y sweep at 93, and providing a 43.51 kHz pulse train at 95 to the x sweep clocking, whereby the x sync moves rightwardly as seen in FIG. 4 for the next slice. The pulse 95 feeds an AND gate 96 feeding a 6 bit counter 97 which counts the 64 intervals corresponding to the start sync band, and then through an invertor 98, the gate 96 is inhibited, and the same output is linked at 101 to enable an AND gate 102 gating to a 10 bit counter 103 which counts the 819 sweep slices of each sector. The output of the counter 103 is inverted at 104 to inhibit the gate 102, and also through link 105 to enable AND gate 106 which gates to a 5 bit counter 107 which counts the 32 slices constituting each sector sync. The output of the counter 107 passes to an invertor 108 which inhibits the gate 106, and operates a one shot multivibrator 109. The multivibrator 109 enables an OR gate 111 which resets the counter 103 through link 114, and counter 107 through an edge delay line 112 and link 113. The multivibrator 109 also feeds a three hit counter 115 of four count capacity to gate an AND gate 116 which feeds a 6 bit counter 117 which counts the 64 intervals in the end sync band 76 at the rightward end of the x sweep excursion. The output of the counter 117 resets at 118 all of the x sweep functions, and a pulse along the link 120 starts the re trace of the x sweep and blanks the cathode ray tube scanner. The x sweep is started by a 42.51 kHz pulse 95 to an AND gate 100, in conjunction with a pulse from an OR gate 99 gated by the counter 97.

Referring again to FIG. 5, in order to enhance the detector response from the record, the track pattern is substantially different from that disclosed in the above mentioned co-pending application. In the present embodiment, each track has a sync or start gap in a periodic position, and the modulation occurs by moving the position of a second gap in relation to it. While the reference gaps are all in a periodic position in space on the record, the scan may not be that precise that the modulation gap could be used alone against a precisely clocked start pulse. Without a great precision in the deflection of the scanner this could not provide the low noise and accurate modulation of the scanned sample light pulse position. The reference gap is used to control the deflection sweep by locking it to the clock system through position feedback by comparing the reference pulses with the clock. The light pulses are then able to operate a pulse width or position discriminator similar in action to that used in the above mentioned application. Because of the slow decay of the phosphor, a transversal filter is used to differentiate the light output of the photodetector providing pulses coincident with the rising edges of the gaps as represented by the sampling light pulses. The minimum gap spacing chosen (50 microns) represents for the scanning rates selected, a time separation of only just under 10 nanoseconds. Thus, without a transversal filter, the system would be inoperable, and with a practical version of the filter, the scan rate is at approximately maximum. It may be observed that the photodetector chosen does not contribute to the response speed limits, as it is capable of much faster operation, and in this regard, the use of the filter is substantially different from that disclosed in the above mentioned co-pending application. The sync comparator 28 (FIG. 1) which receives signals both the photodetector and the timing chain module 14 performs the above described function.

FIG. 7 illustrates the real time convertor 38 in greater 8 detail. The function of this structure is to enable digital information to alternately flow into one or another of two memory register sets, so that one may be loaded, while the other is unloaded to create a continuous flow of digital information, which is subsequently converted back to analog data. Each set of shift registers is loaded with data from the analog to digital converter which passes through an 8 bit plus sign digital adder 125. This adder permits the addition of later selected track segments to be added to the segments previously sampled without loss or disturbance of data. The memory shift register set thus is unloading the just previously loaded sector data during each subsequent sector scan. The adder accomplishes thesimple addition of later selected data permitting the coincident reproduction of data from any sectors. After five such loading cycles, the shift register set is transferred durng the synchronizing interval from load operation at sampling rate to unload operate at real time clock rate by the AND gates 126 and 127 to the registers 128 and 129, in cooperation with load clock 129 which controls gates 130 and 131, and readout gates 132 and 133 controlled by real time clock 134. Each of the parallel registers in both A and B sets are 819 bits long. The load clock is synchronized to the fast scan. Unloading, however, is 5 5/16 times slower and is controlled by the readout clock 134 operating at real time, i.e., a l/l0 second rate. Thus, all data which has accumulated during the H10 second period during which the register was loaded, is simultaneously available at readout time. The unload gates 135 and 136 are also controlled by memory control logic 130, which also controls the sync and section 1 inhibit gates 137 and 138 which in turn control the digital adder 125. The shift register sets each have one register that has a 1 bit index value to mark the start of the 819 bit cycle. This index register acts as a cycle counter. The memories are cleared by the adder during the first sector operation because of the presence of the sector 1 inhibit pulse which effectively adds only zero to the new input data.

Referring to FIG. 10, the timing chain and track select system module 14 which controls the sweep drive 15 and the highly regulated CRT power supply 16 is illustrated in greater detail. Track select data from the control computer is supplied by a data buss 141 which feeds through a link 142 to a sector select command register 143. The register 143 unloads to a sector select register comparator 144, the output 145 of which ANDs to a gate 146. Track selection data is also fed through a link 147 to a track select command register 148 which unloads to a track select register comparator 149, the output of which also ANDs to gate 146. Enabled gate 146 is linked by 150 to a multiplexer 151 having a single line data in and an n" channels out to channel sampling gates 152.

Control computer data in the form of output address is carried by a data buss 132 to the multiplexer, whereby the output of selected tracks is gated to correct sample gates governing multiple output channels. The track count state is fed to comparator 149, and the sector counter state is fed to the comparator 144. Track count state is also fed to the computer to synchronize command timing to the track selection data. Thus, where multiple output channels are provided responsive to individual commands for data related to the multiple output channels, it is possible to respond to each command serially in the order in which the required data is reached during a single complete sweep of the record.

At this point in the disclosure, it is considered advantageous to review the major timing events which occur during operation. The modulation occurring during the crossing of a single track occurs during a period of 106.4038067 nanoseconds. During this time, the scanning beam crosses-one band 74 (FIGS. 4 and one band 75 and arrives at the next band 74. Each vertical slice (y scan) is divided into 216 virtual track periods. The track period frequency is 9.398160 Ml-lz.

During a single slice of the scanning operation, (y sweep) the end of the sweep is triggered by the 201st count in the track counter, with phase lock to the timing chain module. This period is derived from the 4,351 slices per complete scan. There are 64 start and end slices, 32in each of the four bands between the five sectors, and 819 in each sector. The slice frequency in scanning is therefore 43.51 KHz.

The scanning of a single sector requires 18.823259 milliseconds 'for' 819 slices added to 1470.9262 microseconds for the 64 slices at the start of the scan. During one complete scan, all sectors are sampled and memory loaded with data required for output during the next millisecond period. Maximum cueing time is therefore less than 100 milliseconds. If prior scan occurred in a previous sector, then the contents are simultaneously clocked out at the real time rate over the 100 millisecond period. Real time output is at a 500 millisecond rate, and encompasses the output of five cycles of scan over each of the five sectors.

I wish it to be understood that I do not consider the invention limited to the precise details of structure shown and set forth in this specification, for obvious modifications will occur to those skilled in the art to which the invention pertains.

I claim:

1. In a data storage and retrieval system, a data record including at least one elongated track, scanning means progressively orthogonally scanning said track and passing a radiant energy beam through energytransmissive portions of said track, energy detector means disposed on an opposite side of said record, and pulse width modulation means receiving the output of said energy detector means; said track comprising a first undulating elongated energy-transmissive area, second and third elongated non-energy-transmissive areas bordering said first area, and a fourth rectilinear energy-transmissive area bordering one of said second and third areas; whereby orthogonal scanning of said track may create a pulse width modulated signal determined by the instantaneous orthogonal spacing between said first and fourth elongated areas.

2. Structure in accordance with claim 1, further characterized in a sweep drive means controlling the defiection of said scanning means, track pulse counter means operated by the crossing of a scanning beam of said first mentioned area, timing chain means regulating said sweep drive, sync comparator means receiving an output from said track pulse counter means and said timing chain means, and providing a regulatory output signal to said sweep drive.

3. Structure in accordance with claim 1, including transversal filter means sensing the leading edge of each radiant energy pulse formed by the passing of radiant energy beams through each of said first and fourth areas, and employing the detection of the start of the fourth area to determine pulse width.

Claims (3)

1. In a data storage and retrieval system, a data record including at least one elongated track, scanning means progressively orthogonally scanning said track and passing a radiant energy beam through energy-transmissive portions of said track, energy detector means disposed on an opposite side of said record, and pulse width modulation means receiving the output of said energy detector means; said track comprising a first undulating elongated energy-transmissive area, second and third elongated non-energy-transmissive areas bordering said first area, and a fourth rectilinear energy-transmissive area bordering one of said second and third areas; whereby orthogonal scanning of said track may create a pulse width modulated signal determined by the instantaneous orthogonal spacing between said first and fourth elongated areas.

2. Structure in accordance with claim 1, further characterized in a sweep drive means controlling the deflection of said scanning means, track pulse counter means operated by the crossing of a scanning beam of said first mentioned area, timing chain means regulating said sweep drive, sync comparaTor means receiving an output from said track pulse counter means and said timing chain means, and providing a regulatory output signal to said sweep drive.

3. Structure in accordance with claim 1, including transversal filter means sensing the leading edge of each radiant energy pulse formed by the passing of radiant energy beams through each of said first and fourth areas, and employing the detection of the start of the fourth area to determine pulse width.

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