CA1052907A - Reproduction of optical sound tracks - Google Patents
Reproduction of optical sound tracksInfo
- Publication number
- CA1052907A CA1052907A CA232,927A CA232927A CA1052907A CA 1052907 A CA1052907 A CA 1052907A CA 232927 A CA232927 A CA 232927A CA 1052907 A CA1052907 A CA 1052907A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- scanning
- track
- level
- scan
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/02—Analogue recording or reproducing
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/24—Signal processing not specific to the method of recording or reproducing; Circuits therefor for reducing noise
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/002—Recording, reproducing or erasing systems characterised by the shape or form of the carrier
- G11B7/003—Recording, reproducing or erasing systems characterised by the shape or form of the carrier with webs, filaments or wires, e.g. belts, spooled tapes or films of quasi-infinite extent
- G11B7/0032—Recording, reproducing or erasing systems characterised by the shape or form of the carrier with webs, filaments or wires, e.g. belts, spooled tapes or films of quasi-infinite extent for moving-picture soundtracks, i.e. cinema
Abstract
ABSTRACT
A variable area sound track is scanned laterally to derive width-modulated pulses which can be demodulated to audio.
In order to eliminate the effect of noise on the clear area of the track, each said pulse is initiated by a black-to-clear transition sensed in the scanning but is terminated independently of the signal sensed during scanning, namely at reference instants of time.
A variable area sound track is scanned laterally to derive width-modulated pulses which can be demodulated to audio.
In order to eliminate the effect of noise on the clear area of the track, each said pulse is initiated by a black-to-clear transition sensed in the scanning but is terminated independently of the signal sensed during scanning, namely at reference instants of time.
Description
105'~907 The present invention relates to the reproduction of variable area optical sound tracks. Conventionally, such tracks are scanned using a narrow slit of light and a photoelectric cell to generate a signal corre-sponting to the width-modulation of the variable area track. By magnetic recording standards, the signal to noise ratio of optical sound tracks is -poor. Thus considerable problems lie in the way of extending the optical technique to multi channel reproduction.
U.S. patent specification 2,347,084 describes a system in which the track is repeatedly scannet across its width with a very small scanning spot. A photoelectrically generated signal is then essentially a two-level signal whose duration corresponds to the width of the track. By integrating this signal with a suitable time-constant, it may be converted into an amplitude-varying audio signal. This known system goes some way to dealing with the problem of noise on variable area tracks, which usually takes the form of dark spots (dust, flakes due to film abrasion) on the clear area of the track or other variations in density of this area. The black areas flanking the track are comparatively noise-free. By limiting the two-level signal before it is integrated or otherwise demodulated, much noise is eliminated but some dark spots on the clear area will still introduce noise.
One object of this invention is to provide an improved system which effects an even better rejection of noise. Another object is to pro-vide a system which is especially suited to reproduce dual bilateral tracks with reduced noise. It is a further object to effect multi-channel repro-duction with reduced noise.
According to the present invention, there is provided a scanning system for reproducing a variable area optical sound track, comprising scanning means arranged to scan repeatedly across the width of the track to provide a two-level first electrical signal, a bistable circuit for providing a second electrical signal, means for setting the bistable circuit, thereby to set the second signal from a first level to a second level, by a transition in the first signal occurring as the scanning means scan from an opaque area to a clear area of the track and means for resetting the bistable circuit, ~t~
105'~9~7 thereby to reset the second signal from the second level to the first level, at reference instants independently of the first signal.
Since the second signal is set to the second level at a black-to-clear transition and the black area is much more noise-free than the clear area, the leading edge of the pulse at the second level is accurately timed in relation to the edge of the track. On the other hand, the reset to the first level is independent of the first signal. Noise in the clear area is thus completely ignored. With simple bilateral tracks the reset may be accomplished at the end of the scan. With dual-bilateral tracks, in which there are two black-to-clear transitions per scan, the reset can be accomplished by reference pulses synchronised to the scanning means. With such dual-bilateral tracks, which are most often used, the reference pulses can be regarded as corresponding to the scanning of hypothetical reference lines at the edge of and between the two bilateral tracks and parallel to the length of the track. -The second level pulses have a duration representing the track width from a black-to-clear edge to the next hypothetical reference line.
As explained below, steps may be taken to ensure that these lines are positioned in predetermined locations, for instance exactly at the edge and down the centre of the track. Variation hn position of the reference line may result in waveform distortion due to clipping of highly modulated _3_ '' ' '' "' ' . ~' .
105'~907 signals. The variation in depth of modulation of the amplitude-varying audio signal may be derived in known manner from the second signal by integration or other techniques for demodulating width-modulated pulses.
In order to reproduce multi-channel tracks, it is necessary only to use timing gates to select the channel signals from the appropriate tracks.
Although, for simplicity, some described embodiments of the invention use flying spot scanning, it will be appreciated that this method is not essential. As is well known, scanning may either be on the illuminat-ing side with full aperture photo-electric pick-up, as is the case using a flying spot scanner, or may be on the pick-up side with full aperture illumin- ~ -ation, as is the case for example when using a Vidicon scanner. In addition, there are many known techniques, electronic and non-electronic, for generating the scanning movement, including mechanical-optical technlques such as those using rotating or oscillating prisms or mirrors or Nipkow discs. Systems of this nature may be preferred to the described use of a flying spot scanner because of the difficulty of obtaining adequate spot brightness at the high resolution required. It is also possible to scan on the input side with a laser beam deflected, say, by a piezo-electric deflector.
The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a schematic diagram of a basic scanning system;
Figure 2 illustrates a bilateral sound track;
Figure 3 illustrates waveforms for one way of scanning the sound track;
Figure 4 is a block diagram of a first embodiment of the invention operating in accordance with Figure 3;
Figure 5 illustrates waveforms for another way of scanning the sound track;
Figure 6 illustrates a dual bilateral stereo sound track;
Figure 7 illustrates waveforms for scanning the dual track;
Figure 8 is a block diagram of part of a second embodiment of the invention for use with a dual track; and ~OS'~907 Figure 9 illustrates a modified scanning system.
Figure 1 shows a scanning system in which a CRT flying-spot scanner 10 is subjected to X-deflection only under the control of a sweep circuit 12 synchronised to a timing pulse generator 14. The required scanning frequency is several times the highest audio frequency handled - e.g. it may be in the range 30 kHz - 100 kHz. An image of the flying spot is focused on the sound track 16 of a film 18 by a lens 20 to form a transverse scan, the film being fed longitudinally in conventional manner. Light passing through the sound track falls on a photo-electric cell 22 whose output at terminal 24 constitutes the aforementioned first signal.
Figure 2 illustrates a mono bilateral sound track 26 with the line 28 of the scanning spot marked thereacross. The two edges of the track are labelled 1 and 2 where they are traversed by the scanning line 28.
Referring to Figure 3, if the sweep waveform (a) applied to the flying-spot scanner is a sawtooth waveform, (with blank mg on flyback), the photo-electric cell output will be as shown at (b) with the points 1 and 2 marked in correspondence with Figure 2 and with fluctuations illustrated to represent the noise on the clear part of the track. The timing generator 14 can also generate timing reference pulses (c) which are assumed in this example to coincide with the scanning of a hypothetical reference line 30, down the edge of tho track 26 in Figure 2. A second signal (d) (Figure 3) consists of pulses which commence with the black-to-clear transitions 1 of the first signal (b) and terminate with the reference pulses (c), whereby all modulation to the right of the transition 1 is ignored or blanked out, includ-ing the clear-to-black transition 2 and the black area thereafter. The pulses (d) will have a duration representing the track width but which duration is entirely uninfluenced by the fluctuations in signal (b).
Figure 4 illustrates an embodiment of the invention operating in accordance with Figure 3. The signal (b) from terminal 24 is applied through an input amplifier 32 and an optional linearity circuit 34 to a low-pass filter 36. The circuit 34 can correct for non-linearity of the cell 22 and/or the film 18 to minimise noise and distortion. The filter 36 attenuates ~05'~907 spurious low-level, high-frequency noise due to grain, dust and abrasion. The filter has a cut-off frequency of several hundred kHz and may be linear or non-linear in action.
The output from the filter 36 may be applied directly to a differ-entiator 38, but it is preferred to include further circuitry which deals with possible noise in the black area. Although there may be virtually no black-area noise in a virgin film, this will no longer be the case in a worn film, and a white scratch in the black area could appear erroneously to be the edge 1. For this reason, the output of the filter 36 is applied to a delay circuit 37 with a very short delay, the outputs of the circuit 37 and of the filter 36 are applied to an AND gate 39 and the output of the gate 39 is applied to the differentiator 38. The output of the gate 39 will not go true until the scanning spot has moved off the edge 1. In the case of a white fleck in the black area, when the output of the delay circuit 37 goes true, the output of the filter 36 will have reverted to false and the output of the gate 39 will remain false.
The pulsesfrom the differentiator 38 at transitionsll of Figure 3 (b) set a bistable circuit 40 which acts as a blanking circuit. The circuit is re-set at the end of the scanning line by the reference pulses (c) provided from the timing generator 14 via a pulse shaper 44. With dual-bilateral tracks, delay means 42 is additionally used, in order to provide reference pulses between the two halves of the track. The bistable circuit 40 provides the second signal Figure 3~d) and this is applied to an integrator 46 or other suitable pulse-width demodulator. The demodulated signal is corrected for slit-loss by an equalizer 48 giv mg high-frequency boost and the output signal at terminal 50 is available for audio reproduction.
Figure S illustrates the alternative use of a symmetrical triangular scanning waveform (a) to scan in alternate directions across the sound track so that both edges 1 and 2 are utilized. Waveform (b) is the first signal (PEC output) while waveform (c) is waveform (b) differentiated. The bistable circuit 40 is assumed to respond only to positive pulses and is, therefore, set by the pulses shown at (d). The reference pulses (e) are now 105~907 taken to occur at the start of each scan. Referring to Figure 4, the pulses from the generator 14 are applied direct to the reset input of the bistable circuit 40.
Figure 6 is similar to Figure 2 but shows a dual-bilateral track layout in which the two halves are separately modulated to form a two-channel stereo sound track 58 with left and right tracks 60 and 62. The scanning line now crosses edges 1, 2, 3 and 4. Figure 7 shows how these may be scanned using a sawtooth sweep (a). The PEC output appears as at (b~. Left and right channel gate signals (c) and (d) can be generated in synchronism with the scanning waveform and used to gate out left and right channel outputs (e) and ~f) from the signal (b). Each of the signals (d) and (e) can now be dealt with as already described using the circuitry of Figure 4, duplicated for the two channels.
The system of Figure 7 can be extended analogously to Figure 5 and, if the two directions of scan are denoted A and B as in Figure 5, it is possible to gate out separately the left channel A scan signal, the left channel B scan signal, the right channel A scan signal and the right channel B scan signal. As will be seen, such separate treatment is advantageous for mono dual-bilateral tracks. The circuits required are illustrated in Figure 8 as four gates 64 fed by four cyclically interleaved gating waveforms provided by a gating generator 66 synchronised to the timing generator 14. The result-ing four first signals are applied to separate logic circuits and demodulators 68, each of which consists essentially of elements 38, 40 and 46 of Figure 4.
Elements 37 and 39 can also be included in each circuit 68 or can follow the filter 36 to serve all circuits 68. Each circuit 68 is supplied on a line 70 with the appropriate reference pulse for reset of its bistable, in correspond-ence with edges 30 and 31, from the gating generator 66.
For mono dual-bilateral tracks, the circuits 68 provide four redundant signals and these can be applied to a majority circuit 72 which utilizes known techniques to average like signals and leave out of the averag-ing any signal which does not conform substantially to the other three. The output from the circuit 72 feeds the output terminal 50 via the equalizer 48.
105'~907 If the track is a stereo dual-lateral track, then the majority selection technique above cannot be used, since there are effectively only two recordings of each channel. However, the two signals can then be averaged, with some circuit simplification. The gating for each channel can be accomplish-ed by a single gate; similarly one logic and demodulator circuit is used per channel.
Figure 9 illustrates a mechanical scanning system utilizing a segmented disc which may be photographically prepared, for example. The disc 74, driven by a motor 76, has a segmented edge 78 which may have approximately equal clear and opaque areas and is thus much easier to make than a disc with an array of fine scanning holes or slots. The edge 78 is illuminated by a lamp (not shown) and the image thereof is focused on the track 16 by the lens 20 and fixed slit 21. The edge 18 of each segmentation ~of which these may be of the order of several hundred) now moves across the width of the track. By differentiating the output of the photocell 22 in a differentiator 80, the signal at terminal 24 can be made equivalent to that provided by scanning holes, instead of scanning edges. ~-. .
U.S. patent specification 2,347,084 describes a system in which the track is repeatedly scannet across its width with a very small scanning spot. A photoelectrically generated signal is then essentially a two-level signal whose duration corresponds to the width of the track. By integrating this signal with a suitable time-constant, it may be converted into an amplitude-varying audio signal. This known system goes some way to dealing with the problem of noise on variable area tracks, which usually takes the form of dark spots (dust, flakes due to film abrasion) on the clear area of the track or other variations in density of this area. The black areas flanking the track are comparatively noise-free. By limiting the two-level signal before it is integrated or otherwise demodulated, much noise is eliminated but some dark spots on the clear area will still introduce noise.
One object of this invention is to provide an improved system which effects an even better rejection of noise. Another object is to pro-vide a system which is especially suited to reproduce dual bilateral tracks with reduced noise. It is a further object to effect multi-channel repro-duction with reduced noise.
According to the present invention, there is provided a scanning system for reproducing a variable area optical sound track, comprising scanning means arranged to scan repeatedly across the width of the track to provide a two-level first electrical signal, a bistable circuit for providing a second electrical signal, means for setting the bistable circuit, thereby to set the second signal from a first level to a second level, by a transition in the first signal occurring as the scanning means scan from an opaque area to a clear area of the track and means for resetting the bistable circuit, ~t~
105'~9~7 thereby to reset the second signal from the second level to the first level, at reference instants independently of the first signal.
Since the second signal is set to the second level at a black-to-clear transition and the black area is much more noise-free than the clear area, the leading edge of the pulse at the second level is accurately timed in relation to the edge of the track. On the other hand, the reset to the first level is independent of the first signal. Noise in the clear area is thus completely ignored. With simple bilateral tracks the reset may be accomplished at the end of the scan. With dual-bilateral tracks, in which there are two black-to-clear transitions per scan, the reset can be accomplished by reference pulses synchronised to the scanning means. With such dual-bilateral tracks, which are most often used, the reference pulses can be regarded as corresponding to the scanning of hypothetical reference lines at the edge of and between the two bilateral tracks and parallel to the length of the track. -The second level pulses have a duration representing the track width from a black-to-clear edge to the next hypothetical reference line.
As explained below, steps may be taken to ensure that these lines are positioned in predetermined locations, for instance exactly at the edge and down the centre of the track. Variation hn position of the reference line may result in waveform distortion due to clipping of highly modulated _3_ '' ' '' "' ' . ~' .
105'~907 signals. The variation in depth of modulation of the amplitude-varying audio signal may be derived in known manner from the second signal by integration or other techniques for demodulating width-modulated pulses.
In order to reproduce multi-channel tracks, it is necessary only to use timing gates to select the channel signals from the appropriate tracks.
Although, for simplicity, some described embodiments of the invention use flying spot scanning, it will be appreciated that this method is not essential. As is well known, scanning may either be on the illuminat-ing side with full aperture photo-electric pick-up, as is the case using a flying spot scanner, or may be on the pick-up side with full aperture illumin- ~ -ation, as is the case for example when using a Vidicon scanner. In addition, there are many known techniques, electronic and non-electronic, for generating the scanning movement, including mechanical-optical technlques such as those using rotating or oscillating prisms or mirrors or Nipkow discs. Systems of this nature may be preferred to the described use of a flying spot scanner because of the difficulty of obtaining adequate spot brightness at the high resolution required. It is also possible to scan on the input side with a laser beam deflected, say, by a piezo-electric deflector.
The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a schematic diagram of a basic scanning system;
Figure 2 illustrates a bilateral sound track;
Figure 3 illustrates waveforms for one way of scanning the sound track;
Figure 4 is a block diagram of a first embodiment of the invention operating in accordance with Figure 3;
Figure 5 illustrates waveforms for another way of scanning the sound track;
Figure 6 illustrates a dual bilateral stereo sound track;
Figure 7 illustrates waveforms for scanning the dual track;
Figure 8 is a block diagram of part of a second embodiment of the invention for use with a dual track; and ~OS'~907 Figure 9 illustrates a modified scanning system.
Figure 1 shows a scanning system in which a CRT flying-spot scanner 10 is subjected to X-deflection only under the control of a sweep circuit 12 synchronised to a timing pulse generator 14. The required scanning frequency is several times the highest audio frequency handled - e.g. it may be in the range 30 kHz - 100 kHz. An image of the flying spot is focused on the sound track 16 of a film 18 by a lens 20 to form a transverse scan, the film being fed longitudinally in conventional manner. Light passing through the sound track falls on a photo-electric cell 22 whose output at terminal 24 constitutes the aforementioned first signal.
Figure 2 illustrates a mono bilateral sound track 26 with the line 28 of the scanning spot marked thereacross. The two edges of the track are labelled 1 and 2 where they are traversed by the scanning line 28.
Referring to Figure 3, if the sweep waveform (a) applied to the flying-spot scanner is a sawtooth waveform, (with blank mg on flyback), the photo-electric cell output will be as shown at (b) with the points 1 and 2 marked in correspondence with Figure 2 and with fluctuations illustrated to represent the noise on the clear part of the track. The timing generator 14 can also generate timing reference pulses (c) which are assumed in this example to coincide with the scanning of a hypothetical reference line 30, down the edge of tho track 26 in Figure 2. A second signal (d) (Figure 3) consists of pulses which commence with the black-to-clear transitions 1 of the first signal (b) and terminate with the reference pulses (c), whereby all modulation to the right of the transition 1 is ignored or blanked out, includ-ing the clear-to-black transition 2 and the black area thereafter. The pulses (d) will have a duration representing the track width but which duration is entirely uninfluenced by the fluctuations in signal (b).
Figure 4 illustrates an embodiment of the invention operating in accordance with Figure 3. The signal (b) from terminal 24 is applied through an input amplifier 32 and an optional linearity circuit 34 to a low-pass filter 36. The circuit 34 can correct for non-linearity of the cell 22 and/or the film 18 to minimise noise and distortion. The filter 36 attenuates ~05'~907 spurious low-level, high-frequency noise due to grain, dust and abrasion. The filter has a cut-off frequency of several hundred kHz and may be linear or non-linear in action.
The output from the filter 36 may be applied directly to a differ-entiator 38, but it is preferred to include further circuitry which deals with possible noise in the black area. Although there may be virtually no black-area noise in a virgin film, this will no longer be the case in a worn film, and a white scratch in the black area could appear erroneously to be the edge 1. For this reason, the output of the filter 36 is applied to a delay circuit 37 with a very short delay, the outputs of the circuit 37 and of the filter 36 are applied to an AND gate 39 and the output of the gate 39 is applied to the differentiator 38. The output of the gate 39 will not go true until the scanning spot has moved off the edge 1. In the case of a white fleck in the black area, when the output of the delay circuit 37 goes true, the output of the filter 36 will have reverted to false and the output of the gate 39 will remain false.
The pulsesfrom the differentiator 38 at transitionsll of Figure 3 (b) set a bistable circuit 40 which acts as a blanking circuit. The circuit is re-set at the end of the scanning line by the reference pulses (c) provided from the timing generator 14 via a pulse shaper 44. With dual-bilateral tracks, delay means 42 is additionally used, in order to provide reference pulses between the two halves of the track. The bistable circuit 40 provides the second signal Figure 3~d) and this is applied to an integrator 46 or other suitable pulse-width demodulator. The demodulated signal is corrected for slit-loss by an equalizer 48 giv mg high-frequency boost and the output signal at terminal 50 is available for audio reproduction.
Figure S illustrates the alternative use of a symmetrical triangular scanning waveform (a) to scan in alternate directions across the sound track so that both edges 1 and 2 are utilized. Waveform (b) is the first signal (PEC output) while waveform (c) is waveform (b) differentiated. The bistable circuit 40 is assumed to respond only to positive pulses and is, therefore, set by the pulses shown at (d). The reference pulses (e) are now 105~907 taken to occur at the start of each scan. Referring to Figure 4, the pulses from the generator 14 are applied direct to the reset input of the bistable circuit 40.
Figure 6 is similar to Figure 2 but shows a dual-bilateral track layout in which the two halves are separately modulated to form a two-channel stereo sound track 58 with left and right tracks 60 and 62. The scanning line now crosses edges 1, 2, 3 and 4. Figure 7 shows how these may be scanned using a sawtooth sweep (a). The PEC output appears as at (b~. Left and right channel gate signals (c) and (d) can be generated in synchronism with the scanning waveform and used to gate out left and right channel outputs (e) and ~f) from the signal (b). Each of the signals (d) and (e) can now be dealt with as already described using the circuitry of Figure 4, duplicated for the two channels.
The system of Figure 7 can be extended analogously to Figure 5 and, if the two directions of scan are denoted A and B as in Figure 5, it is possible to gate out separately the left channel A scan signal, the left channel B scan signal, the right channel A scan signal and the right channel B scan signal. As will be seen, such separate treatment is advantageous for mono dual-bilateral tracks. The circuits required are illustrated in Figure 8 as four gates 64 fed by four cyclically interleaved gating waveforms provided by a gating generator 66 synchronised to the timing generator 14. The result-ing four first signals are applied to separate logic circuits and demodulators 68, each of which consists essentially of elements 38, 40 and 46 of Figure 4.
Elements 37 and 39 can also be included in each circuit 68 or can follow the filter 36 to serve all circuits 68. Each circuit 68 is supplied on a line 70 with the appropriate reference pulse for reset of its bistable, in correspond-ence with edges 30 and 31, from the gating generator 66.
For mono dual-bilateral tracks, the circuits 68 provide four redundant signals and these can be applied to a majority circuit 72 which utilizes known techniques to average like signals and leave out of the averag-ing any signal which does not conform substantially to the other three. The output from the circuit 72 feeds the output terminal 50 via the equalizer 48.
105'~907 If the track is a stereo dual-lateral track, then the majority selection technique above cannot be used, since there are effectively only two recordings of each channel. However, the two signals can then be averaged, with some circuit simplification. The gating for each channel can be accomplish-ed by a single gate; similarly one logic and demodulator circuit is used per channel.
Figure 9 illustrates a mechanical scanning system utilizing a segmented disc which may be photographically prepared, for example. The disc 74, driven by a motor 76, has a segmented edge 78 which may have approximately equal clear and opaque areas and is thus much easier to make than a disc with an array of fine scanning holes or slots. The edge 78 is illuminated by a lamp (not shown) and the image thereof is focused on the track 16 by the lens 20 and fixed slit 21. The edge 18 of each segmentation ~of which these may be of the order of several hundred) now moves across the width of the track. By differentiating the output of the photocell 22 in a differentiator 80, the signal at terminal 24 can be made equivalent to that provided by scanning holes, instead of scanning edges. ~-. .
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A scanning system for reproducing a variable area optical sound track, comprising scanning means arranged to scan repeatedly across the width of the track to provide a two-level first electrical signal, a bistable circuit for providing a second electrical signal, means for setting the bistable circuit, thereby to set the second signal from a first level to a second level, by a transition in the first signal occurring as the scanning means scan from an opaque area to a clear area of the track and means for resetting the bistable circuit, thereby to reset the second signal from the second level to the first level, at reference instants independently of the first signal.
2. A scanning system according to claim 1, wherein the means for resetting the bistable circuit are responsive to reference pulses synchronised to the scanning means.
3. A scanning system according to claim 2, for use with a bilateral sound track, wherein the scanning means are arranged to scan in alternate directions across the track with the same speed for both directions, the means for setting the bistable circuit is responsive to each transition in the first signal occurring as the scanning means scan from an opaque area to a clear area of the track and following each such transition the bistable circuit is reset by the resetting means in accordance with reference pulses symmetrically timed in relation to the scanning such that the durations of second levels of the second signal arising from scanning opposite edges of the sound track are substantially the same.
4. A scanning system according to claim 1, comprising delay means operative to delay setting of the bistable circuit until a transition in the first signal occurring as the scanning means scan from an opaque area to a clear area of the track is followed by maintenance of the first signal at a level corresponding to a clear area of the track for a predetermined length of time established by the delay means.
5. A scanning system according to claim 1, for use with a plurality of side-by-side tracks, wherein the scanning means is arranged to scan across all tracks in each scan, gating means are provided responsive to the signal provided by the scanning and to gating signals synchronised to the scanning means to provide a separate first signal for each track, and wherein a second signal in generated individually from each first signal.
6. A scanning system according to claim 5, wherein a plurality of more than two redundant second signals are generated and comprising a majority circuit operative to provide an output signal representative of a majority of the redundant second signals.
7. A scanning system according to claim 1, wherein the scanning means comprise means for illuminating the track, means for repeatedly sweeping obturating edges across the path of illumination, photoelectric means responsive to the light passed by the track to provide an electric signal, and means for differentiating the last-said signal to provide said first signal.
8. A scanning system for reproducing a variable area optical sound track, comprising scanning means arranged to scan repeatedly across the width of the track to provide a two-level first electrical signal, a bistable circuit for providing a second electrical signal, means for setting the bistable circuit, thereby to set the second signal from a first level to a second level, by a transition in the first signal occurring as the scanning means scan from an opaque area to a clear area of the track and means operative to reset the bistable circuit, thereby to reset the second signal from the second level to the first level, at an instant occurring when the scanning means has scanned back on to an extended opaque area of the track, thereby to ignore non-extended opaque areas occurring within the clear area.
9. A scanning system according to claim 8, wherein the reset means comprise a circuit synchronised to the scanning means and operative to reset the bistsble circuit at reference instants independently of the first signal.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB37292/74A GB1525691A (en) | 1974-08-27 | 1974-08-27 | Reproduction of optical sound tracks |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1052907A true CA1052907A (en) | 1979-04-17 |
Family
ID=10395313
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA232,927A Expired CA1052907A (en) | 1974-08-27 | 1975-08-06 | Reproduction of optical sound tracks |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4338684A (en) |
| JP (1) | JPS5927971B2 (en) |
| CA (1) | CA1052907A (en) |
| DE (1) | DE2536285C3 (en) |
| GB (1) | GB1525691A (en) |
| IT (1) | IT1041801B (en) |
| NL (1) | NL186277C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2392464A1 (en) * | 1977-05-23 | 1978-12-22 | Dbx | APPARATUS AND METHOD FOR REPRODUCING SOUNDS FROM OPTICALLY RECORDED SOUND SIGNALS |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5059126A (en) * | 1990-05-09 | 1991-10-22 | Kimball Dan V | Sound association and learning system |
| IL96777A0 (en) * | 1990-12-25 | 1991-09-16 | Shmuel Goldberg | General purpose synchronized audio aid system |
| EP0570524B1 (en) * | 1991-02-04 | 1996-01-03 | Dolby Laboratories Licensing Corporation | Storage medium and apparatus for recovering information from such medium by oversampling |
| US5237559A (en) * | 1991-09-05 | 1993-08-17 | Dolby Laboratories Licensing Corporation | Reproduction of sound track signals by varying the detector threshold level as a function of the transverse scan position |
| WO2006000231A1 (en) * | 2004-06-29 | 2006-01-05 | Laser Interface A/S | An optical sound track scanner system |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2025027A (en) * | 1930-03-06 | 1935-12-24 | Radio Inventions Inc | Television system and apparatus |
| US2049384A (en) * | 1930-05-29 | 1936-07-28 | Radio Inventions Inc | System for television and sound |
| US2184525A (en) * | 1936-02-21 | 1939-12-26 | Bell Telephone Labor Inc | Electrooptical scanning apparatus |
| BE447615A (en) * | 1941-08-30 | |||
| US2347084A (en) * | 1942-09-15 | 1944-04-18 | Rca Corp | Noiseless sound system |
| US2538869A (en) * | 1946-03-14 | 1951-01-23 | Hartford Nat Bank & Trust Co | Stereophonic sound |
| US2575445A (en) * | 1948-10-01 | 1951-11-20 | Anthony E Neidt | Scanning of sound records |
| US3138669A (en) * | 1961-06-06 | 1964-06-23 | Rabinow Jacob | Record player using light transducer and servo |
-
1974
- 1974-08-27 GB GB37292/74A patent/GB1525691A/en not_active Expired
-
1975
- 1975-08-06 CA CA232,927A patent/CA1052907A/en not_active Expired
- 1975-08-08 NL NLAANVRAGE7509516,A patent/NL186277C/en not_active IP Right Cessation
- 1975-08-11 IT IT26277/75A patent/IT1041801B/en active
- 1975-08-14 DE DE2536285A patent/DE2536285C3/en not_active Expired
- 1975-08-26 JP JP50103399A patent/JPS5927971B2/en not_active Expired
-
1980
- 1980-04-07 US US06/137,902 patent/US4338684A/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2392464A1 (en) * | 1977-05-23 | 1978-12-22 | Dbx | APPARATUS AND METHOD FOR REPRODUCING SOUNDS FROM OPTICALLY RECORDED SOUND SIGNALS |
Also Published As
| Publication number | Publication date |
|---|---|
| DE2536285A1 (en) | 1976-04-15 |
| JPS5149702A (en) | 1976-04-30 |
| GB1525691A (en) | 1978-09-20 |
| US4338684A (en) | 1982-07-06 |
| IT1041801B (en) | 1980-01-10 |
| NL186277C (en) | 1990-10-16 |
| NL7509516A (en) | 1976-03-02 |
| DE2536285B2 (en) | 1977-12-08 |
| JPS5927971B2 (en) | 1984-07-10 |
| DE2536285C3 (en) | 1978-09-14 |
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