RECORDING SYSTEM FOR SIMULTANEOUSLY PROJECTING PHOTOGRAPHIC IMAGES WITH A RECORDED COMMENTARY
United States Patent 3637950
Method and system for a simultaneous projection of photographic images associated with a recorded commentary. Electrical signals coming from the audio spectrum representing the commentary are recorded and a series of control pulses having a given carrier frequency and occuring at predetermined intervals are superimposed on the signals. The pulses are modulated with a signal having a frequency different from the carrier frequency. A switching means is actuated by detected and amplified modulating signals for actuating a photographic image changing device and short-circuiting a filter connecting a reading device to a loudspeaker.
US Patent References:
Recording and reproducing systems
Vandivere - February 1957 - 2780679
Control mechanism responsive to a recorded signal
Flan et al. - April 1957 - 2787669
System of recording program control signals
Nisbet - February 1967 - 3305645
ELECTRICAL TAPE-SLIDE SYNCHRONIZING SYSTEM
Wright - January 1969 - 3420966
WIDE BAND RECORDING AND REPRODUCING SYSTEM
Warren - December 1969 - 3482038
Recording and reproducing systems
Vandivere - February 1957 - 2780679
Control mechanism responsive to a recorded signal
Flan et al. - April 1957 - 2787669
System of recording program control signals
Nisbet - February 1967 - 3305645
ELECTRICAL TAPE-SLIDE SYNCHRONIZING SYSTEM
Wright - January 1969 - 3420966
WIDE BAND RECORDING AND REPRODUCING SYSTEM
Warren - December 1969 - 3482038
Application Number:
04/755702
Publication Date:
01/25/1972
Filing Date:
08/27/1968
View Patent Images:
Export Citation:
Assignee:
Paul, Claude Marie Touvier-berthet (Lyon, FR)
Primary Class:
Other Classes:
369/70, 369/175, 369/47.190
International Classes:
G03B15/08; G03B31/06; G03B31/00; G11B27/30; G11B23/30; G11B31/00
Field of Search:
179/1.1VC,1.2S,1.2MD,1.1TC 340/174.1K,174.1C
Primary Examiner:
Konick, Bernard
Assistant Examiner:
Eddleman, Alfred H.
Claims:
Having now described my invention, what I claim as new and desire to secure by Letters Patent is
1. A system for reproducing recordings made, in a recording system for a simultaneous projection of photographic images associated with a recorded commentary, such a recording comprising simultaneously recorded thereon, electrical signals coming from the audio spectrum representing said commentary and superimposed to said audio spectrum signals, a series of control pulses of a given carrier frequency and occuring at predetermined time intervals, said control pulses being modulated with signals the frequency of which is different from said carrier frequency, said reproducing system comprising a sound channel having a reading device, a loudspeaker connected to said reading device by means of a filter tuned to said carrier frequency, in order to stop the same, first filtering and amplifying means for passing and amplifying only the carrier frequency signals, second filtering, detecting and amplifying means connected in series with said first filtering and amplifying means for passing, filtering, detecting and amplifying only said modulating frequency signals, switching means actuated by said detected and amplified modulating frequency signals, for actuating a photographic image changing device and for short circuiting said filter connecting said reading device to said loudspeaker upon the absence at the output of said reading device, in said audio spectrum signal of said modulated pulse signals in order to pass to the loudspeaker the part of the audio spectrum corresponding to the frequency of said pulses and for connecting said loudspeaker filter upon the presence in said audio spectrum of said modulated pulse signals in order to prevent said pulse signals to reach said loudspeaker.
2. A system as claimed in claim 1, comprising a series of detecting and amplifying means having outputs respectively connected to distinct switching means, each of said detecting and amplifying means being capable of producing a signal as a function of the appearance of a modulating frequency corresponding to the respective switching means.
3. A system as claimed in claim 1, wherein said switching means comprise a switch actuated by a relay connected to the output of said second filtering, detecting and amplifying means, said switch having a first contact for actuating said photographic image-changing means and a second contact for short circuiting said filter connecting said loudspeaker to said reading device.
4. A system as claimed in claim 2, wherein said distinct switching means comprise switches actuated by respective relays connected to the outputs of said respective detecting and amplifying means.
1. A system for reproducing recordings made, in a recording system for a simultaneous projection of photographic images associated with a recorded commentary, such a recording comprising simultaneously recorded thereon, electrical signals coming from the audio spectrum representing said commentary and superimposed to said audio spectrum signals, a series of control pulses of a given carrier frequency and occuring at predetermined time intervals, said control pulses being modulated with signals the frequency of which is different from said carrier frequency, said reproducing system comprising a sound channel having a reading device, a loudspeaker connected to said reading device by means of a filter tuned to said carrier frequency, in order to stop the same, first filtering and amplifying means for passing and amplifying only the carrier frequency signals, second filtering, detecting and amplifying means connected in series with said first filtering and amplifying means for passing, filtering, detecting and amplifying only said modulating frequency signals, switching means actuated by said detected and amplified modulating frequency signals, for actuating a photographic image changing device and for short circuiting said filter connecting said reading device to said loudspeaker upon the absence at the output of said reading device, in said audio spectrum signal of said modulated pulse signals in order to pass to the loudspeaker the part of the audio spectrum corresponding to the frequency of said pulses and for connecting said loudspeaker filter upon the presence in said audio spectrum of said modulated pulse signals in order to prevent said pulse signals to reach said loudspeaker.
2. A system as claimed in claim 1, comprising a series of detecting and amplifying means having outputs respectively connected to distinct switching means, each of said detecting and amplifying means being capable of producing a signal as a function of the appearance of a modulating frequency corresponding to the respective switching means.
3. A system as claimed in claim 1, wherein said switching means comprise a switch actuated by a relay connected to the output of said second filtering, detecting and amplifying means, said switch having a first contact for actuating said photographic image-changing means and a second contact for short circuiting said filter connecting said loudspeaker to said reading device.
4. A system as claimed in claim 2, wherein said distinct switching means comprise switches actuated by respective relays connected to the outputs of said respective detecting and amplifying means.
Description:
The present invention relates to the projection of photographic images by means of, for example, a projector comprising an automatic image-changing device, the images being projected simultaneously with a recorded spoken commentary or other musical accompaniment, the automatic control being achieved by means of pulses superimposed on the electrical spectrum recorded from said commentary.
A method for recording such a commentary is known in which a certain frequency of the recorded electrical spectrum is eliminated and a pulse having the same frequency is recorded at predetermined intervals, that is, wherever it is desired to change from one photographic image to another during the reading or reproduction of the recording.
A drawback of this method is that, when reading the recorded commentary, the audio spectrum is mutilated since a given frequency has been eliminated from the recorded spectrum and is not reproduced for the audience.
The object of the invention is to remedy this drawback.
The invention provides a recording method for the simultaneous projection of photographic images associated with a recorded commentary, said method comprising recording the electrical signals coming from the audio spectrum representing the commentary, superimposing on said signals a series of control pulses which have a given carrier frequency and occur at predetermined intervals, and modulating said pulses with a signal having a frequency different from the carrier frequency.
Said modulation can be a frequency, amplitude or phase modulation.
The various types of modulation can be effected simultaneously, the modulation frequencies then having if desired different values.
According to a particular feature of the invention, whose purpose is to render the control pulses as inaudible as possible, the amplitude of each of said control pulses follows a decreasing law.
Further features and advantages of the invention will be apparent from the ensuing description with reference to the accompanying drawing.
In the drawing:
FIG. 1 is a simplified diagram of a recording system for carrying out a first example of the method according to the invention;
FIG. 2 is a simplified diagram of a reading system for reading recordings made by means of said method;
FIG. 3 illustrates an embodiment of a reading system showing the utilization of a recording having a plurality of series of control pulses;
FIG. 4 is a diagram illustrating a particular feature of the operation of a relay, this figure facilitating the explanation of the switch shown in FIG. 5, and
FIG. 5 is a diagram of one embodiment of a switch shown in FIG. 1.
FIG. 1 shows a system for recording in accordance with a first example of the method according to the invention. This system comprises a transducer 1 for converting audio vibrations-- produced by the reading of a commentary for example adapted to accompany the projection of a series of diapositive images or lantern slides--into electrical signals. This transducer is connected to a recording device 2 which can operate according to any principle, such as for example that of magnetic tapes, phonograph discs, or optical films.
The recording system also comprises an oscillator 3 delivering a carrier signal of any electrical frequency (Fp).
The oscillator 3 is modulated by a second oscillator 4 producing a modulating signal whose electrical frequency (Fm) is necessarily different from the carrier frequency (Fp). Thus, the signal issuing from the oscillator 4 modulates, that is, varies the phase, frequency or amplitude of the signal from the oscillator 3. This group of signals is applied to the input of the recording device 2 through switch means 5 whereby it is possible to apply only constant duration pulses of the modulated signal. The latter, which is mixed with the signals from the transducer, therefore forms the complex signal which is recorded by the recording device 2 on a support suitable for this operation such as, for example, a magnetic tape, a photograph disc, an optical film, or the like.
The frequencies employed by the oscillators 3 and 4 can have any values. However, they cannot be identical. By way of example, and in order to permit the reproduction by means of conventional reading or reproducing apparatuses, the carrier frequency Fp could be chosen to be 8,000 Hz. and the modulating frequency Fm to be 50 Hz. Thus, the modulation of Fp could be chosen to be one of amplitude by the frequency Fm. FIG. 2 shows a reading system for the signal recorded by the recording system shown in FIG. 1.
This system comprises a reading apparatus proper 6, such as a record player if the recording has been effected on a phonograph disc for example, a tape recorder if a magnetic tape has been used, etc. The output of the reading apparatus 6 is connected to a filter 7 whose resonance is tuned to the frequency of 8,000 Hz. in the chosen example.
This filter consists of an inductance coil S1 and a capacitor C1. It has a maximum impedance at its resonant frequency and is therefore capable of opposing the transmission to a loudspeaker 8 connected thereto, frequencies of value Fp, namely 8,000 Hz. in this example. Now, the filter 7 is short circuited by a switch 9 the action of which will be described hereinafter. The speaker 8 therefore receives all the recorded signals with elimination of no frequency and complete fidelity of the recording is therefore achieved.
Further, the output of the reading apparatus 6 is connected to a filter 10 whose resonant frequency is tuned to the frequency Fp (8,000 Hz.). This filter 10 consists of an inductance coil S2 and a capacitor C2 and is connected in such a manner that it has a minimum impedance at its resonant frequency and therefore only transmits a narrow band of frequencies centered on the frequency Fp to an amplifier 11 connected thereto. These signals are thus amplified at the output of the amplifier 11 and applied to a filter 12 also tuned to the frequency Fp, this filter consisting of an inductance coil S3 and a capacitor C3, whereby to improve the selectivity of the system, that is the capacity to separate the frequencies applied to the filter 10. The signals of frequency Fp available on the filter 12 are received by a winding 13 and then transmitted to an amplitude detector 14 whose function is to eliminate the carrier frequency Fp and make the modulating signal Fm appear. This signal of frequency Fm, namely 50 Hz. in the presently described example, is then applied to another amplifier 15 which is connected to a filter 16 consisting of an inductance coil S4 and a capacitor C4. This filter 16 is tuned to the value of the frequency Fm. The signal of frequency Fm available at the filter 16 is received by a winding 17, coupled to the winding S4, and thereafter rectified by a diode 18, that is converted into a DC voltage which is again amplified by an amplifier 19 and applied to an electromagnet 20 which it is capable of energizing.
The electromagnet 20 actuates the switch 9 and another switch 21. When closed by the action of the electromagnet 20, the switch 21 controls an image-changing device 22 of a projector (not shown), which is the desired function in the presently described example. When opened by the action of the electromagnet 20, the switch 9 opens the short circuit of the filter 7 and the latter then opposes the transmission to the speaker 8 of the signals which had initiated the control or actuation of the device 22. These signals are consequently not perceived by the audience.
This system operates in the following manner:
If a signal of frequency Fp is read by the reading or reproducing device, there are two possibilities:
1. This signal comes from a sound of the commentary and must not initiate the actuation of the image-changing device 22; it must therefore be perceived by the audience.
Being of suitable frequency, this signal is not stopped by the filter 10, is amplified by the amplifier 11 and available on the filter 12. It is received by the winding 13 and transmitted to the diode 14. But as it does not have the modulating frequency Fm, its detection does not result in a suitable signal capable of passing through the amplifier 15 and no signal appears on the filter 16 and nothing can be received by the winding 17. No voltage is applied to the diode 18 and no voltage is therefore transmitted to the amplifier 19 which cannot energize the electromagnet 20. The switch 21 remains open and does not actuate the changing device 22. The switch 9 remains closed and still short circuits the filter 7 and consequently the sound of frequency Fp can be reproduced by the speaker 8.
2 . This signal comes from a pulse of the oscillator 3 (FIG. 1) modulated by the oscillator 4 and must therefore actuate the changing device 22 without being perceived by the audience.
As this signal is of suitable frequency it is not stopped by the filter 10 and is amplified by the amplifier 11 and available on the filter 12. It is received by the winding 13 and transmitted to the diode 14. As this signal comprises the frequency Fm its detection results in a signal of frequency Fm at the input of the amplifier 15 and this amplified signal appears at the filter 16 and is received by the winding 17. The signal is rectified by the diode 18 and a DC voltage appears at the input of the amplifier 19. When amplified, this voltage is applied to the electromagnet 20 which it actuates. The switch 21 closes and actuates the changing device 22, the switch 9 opens and causes the filter 7 to operate and the latter opposes the transmission to the speaker 8 of this signal of frequency Fp. The signal consequently remains inaudible to the audience since it is not reproduced by the speaker.
The actuation of the changing device 22 therefore requires a double information, namely the reading of a frequency Fp and the modulation of this frequency by another frequency Fm. The application of either of these frequencies alone results in no reaction. The application of frequency Fp alone resumes the first possibility described hereinbefore and a signal having the frequency Fm alone cannot pass the filter 10.
It should be mentioned that the simultaneous application of two distinct frequencies, one of value Fp and the other of value Fm, cannot satisfy the complete detection. These frequencies must be in close relationship according to the type of detection employed. This relationship is a modulation of the amplitude of frequency Fp by the frequency Fm, which is the relationship chosen in the example shown in FIG. 2 (diode 14), a modulation of the frequency Fp by Fm, or a modulation of the phase of Fp by Fm.
It should also be noted that the frequency Fm cannot be reproduced by the speaker 8 since this frequency does not appear at the output of the reading apparatus 6. The appearance of frequency Fm essentially implies a detection of Fp appropriate to the modulating method employed when recording in accordance with the system shown in FIG. 1.
It will be understood that the reading system described hereinbefore employs a recording consisting of a complete audio spectrum having at certain intervals a pulse of frequency Fp modulated by a frequency Fm, these pulses resulting in the changing of diapositive images or lantern slides. The frequency Fp is therefore only eliminated from the audio spectrum perceived by the audience when a control pulse is produced. In practice, this spectrum can be considered as being fully transmitted.
However, it is possible to record several types of control pulses modulated with distinct frequencies, which serve in the reading system after filtering in particular filters, too obtain several control signals, these pulses for example starting up a second projector or lighting up the projecting room. These pulses can of course be modulated in different ways.
One embodiment of such a reading system is shown in FIG. 3. In this diagram, the reproducing channel and the filters and relay contacts have been omitted for reasons of clarity.
The control signals received in a reading device 30 are transmitted to a first filter of frequency Fp, namely filter 31. Its output signal is transmitted, detected and filtered in three separate channels, 32, 33 and 34 (Fm1, Fm2, Fm3) controlling relays 35, 36 and 37 respectively, the latter serving to control a first projector, start a second projector when the first has used up a batch of diapositive images or lantern slides and light up the room at the end of the commentary.
It will be observed that the carrier frequency is modulated in amplitude by the frequency Fm1 and modulated in frequency by the frequencies Fm2 and Fm3. A discriminator 29 detects the latter frequencies.
With reference to FIG. 4, which has been given only by way of example, a few properties of an electromagnetic relay will now be recalled.
A relay R is fed by a battery B through a potentiometer P. The potentiometer varies the intensity of the energization current of the relay R. It is observed that the intensity required for holding the relay exceeds the intensity, when the energization is no longer sufficient, at which the relay is released. Consequently, the relay can be operated by energizing it with a pulse of given current density (point x). It is observed that the relay remains energized with a much smaller intensity (point y).
This feature of relay operation can be employed in the method according to the invention. Indeed, according to a particular feature of the invention, the purpose of which is to render the control pulses as inaudible as possible when reproducing, the amplitude of each of these pulses follows a decreasing law. The control relay 22 (FIG. 2) is energized at the start of the pulse and maintained in this position by the rest of the pulse until the amplitude at which the energization can no longer be maintained is reached.
It will be understood that, in this way, the pulse, while it has an action identical to that of pulses of constant amplitude, is less perceptible to the audience, on one hand because the pulse appears to be of shorter duration to the listener, and, on the other hand, because as the ear is very sensitive to sudden variations in the perceived spectrum, one of the variations has become very regular, namely the variations which puts a stop to the pulse.
One embodiment, by which the invention is not intended to be limited, of a device for obtaining control pulses having a decreasing law is shown in FIG. 5. This device is no other than a special form of the switch 5 shown in FIG. 1 and comprises a capacitor 38, one terminal of which is earthed and the other connected to the junction point of two resistors 39 and 40. A pushbutton 41 is connected in parallel with the capacitor 38. The resistor 40 is connected in series with a polarization battery 42 whose positive terminal is earthed. The resistor 39 is connected to the input 43 of the device (connected to the output of the oscillator 3 shown in FIG. 1) and to the grid of a triode 44 connected as an amplifier. The anode of the triode is connected in series with an anode resistor 45 and a battery 46, and to the output terminal 47 of the switch, which is connected to the recording device 2 (FIG. 1).
While the pushbutton 41 is open, the triode 44 is turned off by the polarization voltage supplied by the battery 42, the capacitor 38 being charged. The signal from the oscillator 3 (FIG. 1) therefore cannot pass through the triode and reach the recording device 2.
When it is desired to record a control pulse, that is, change from one diapositive image or lantern slide to another, the pushbutton 41 is actuated in such a manner that the capacitor 38 is discharged instantaneously. The triode can therefore amplify the signal applied to its grid, the latter having the potential of the earth. However, the capacitor is charged progressively so that the triode is polarized progressively until turned off. The output pulse therefore follows a decreasing law.
Note that a recording effected in accordance with the method of the invention can be read or reproduced if desired with a reading or reproducing system adapted to reproduce recordings made in accordance with the conventional method described hereinabove.
However, in this case, one condition must be satisfied when recording. The electrical signal must be slightly attenuated at the carrier frequency Fp so that a sound, normally emitted during the commentary at this frequency and having a sufficiently high amplitude level, does not accidentally cause the image-changing relay to respond. Further, the pulses must be recorded by means of the device described with reference to FIG. 5 so as to render them as little audible as possible. The image-changing relay is then energized by the start of the pulse and will remain energized practically until its disappearance. The modulation frequency Fm in this case is not detected.
However, it will be observed that the level of the control pulse can be lower in this case, and consequently less audible, if its modulation is effected in amplitude for a given sensitivity of the control relay. Indeed, as the modulation frequency is not perceptible in the speaker of the conventional system since no detection is effected, it is however superimposed on the DC current resulting from the detection of the signal Fp of the control pulse. The pulse of the current which actuates the control relay is an undulating current whose crests are higher than in the case where unmodulated pulses would be recorded (the case of a conventional recording method). Consequently, the recording according to the invention can be read or reproduced in conventional reproducing systems, it being possible for the control pulses to have a much higher amplitude at the frequency Fp than they have in recordings made in accordance with the conventional recording method. The pulses will therefore be less audible.
An example, by which the invention is not intended to be limited, will now be given of a recording made by the method according to the invention. This recording can be reproduced with the conventional reproducing system and with the system according to the invention, the control part of which is shown in FIG. 3.
The recording made with a system including the switch shown in FIG. 5 is made under the following conditions:
The sound channel employed has a range of 20-50,000 Hz. The images are changed by control pulses obtained from a signal of 7,000 Hz. which is 100 percent amplitude modulated by a frequency of 50 Hz. The pulses exhibit a decreasing amplitude. Changing from the first projector to the second projector, after the batch of diapositive images or lantern slides of the second projector has been used up, is effected by means of a control pulse of 7,000 Hz. which is frequency-modulated by a signal of 100 Hz. and amplitude modulated at 50 Hz. A control pulse of 7,000 Hz. frequency-modulated by a signal of 400 Hz. is recorded for automatically lighting up the projecting room.
During the reproduction in a reading or reproducing system designed in accordance with the conventional method, the control pulses of 7,000 Hz. modulated with a signal of 50 Hz., change the images, the control relay of the image-changing device being energized at the start of the pulse by the maximum amplitude and maintained in its energized position by the rest of this control pulse of decreasing amplitude. The pulses of 7,000 Hz. frequency-modulated at 100 Hz. and at 400 Hz. are ineffective since, as they have not been modulated in amplitude, their amplitude is insufficient to actuate the relay.
It should be mentioned that the frequency of 7,000 Hz. cannot reach the audience since a filter is provided in the reproduction channel.
During the reproduction in a system according to FIG. 3, the pulses control respectively:
at 7,000 Hz. with amplitude modulation 50 Hz. (Fm1), the relay 1; image changing,
at 7,000 Hz. with frequency modulation (Fm2) the relay 2; the connection and starting up of the second projector, the first projector being put out of operation,
at 7,000 Hz. with frequency modulation at 400 Hz. (Fm3)--the relay 3 alone is energized and the lights in the projecting room are turned on.
Although specific embodiments of the invention have been described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claims.
A method for recording such a commentary is known in which a certain frequency of the recorded electrical spectrum is eliminated and a pulse having the same frequency is recorded at predetermined intervals, that is, wherever it is desired to change from one photographic image to another during the reading or reproduction of the recording.
A drawback of this method is that, when reading the recorded commentary, the audio spectrum is mutilated since a given frequency has been eliminated from the recorded spectrum and is not reproduced for the audience.
The object of the invention is to remedy this drawback.
The invention provides a recording method for the simultaneous projection of photographic images associated with a recorded commentary, said method comprising recording the electrical signals coming from the audio spectrum representing the commentary, superimposing on said signals a series of control pulses which have a given carrier frequency and occur at predetermined intervals, and modulating said pulses with a signal having a frequency different from the carrier frequency.
Said modulation can be a frequency, amplitude or phase modulation.
The various types of modulation can be effected simultaneously, the modulation frequencies then having if desired different values.
According to a particular feature of the invention, whose purpose is to render the control pulses as inaudible as possible, the amplitude of each of said control pulses follows a decreasing law.
Further features and advantages of the invention will be apparent from the ensuing description with reference to the accompanying drawing.
In the drawing:
FIG. 1 is a simplified diagram of a recording system for carrying out a first example of the method according to the invention;
FIG. 2 is a simplified diagram of a reading system for reading recordings made by means of said method;
FIG. 3 illustrates an embodiment of a reading system showing the utilization of a recording having a plurality of series of control pulses;
FIG. 4 is a diagram illustrating a particular feature of the operation of a relay, this figure facilitating the explanation of the switch shown in FIG. 5, and
FIG. 5 is a diagram of one embodiment of a switch shown in FIG. 1.
FIG. 1 shows a system for recording in accordance with a first example of the method according to the invention. This system comprises a transducer 1 for converting audio vibrations-- produced by the reading of a commentary for example adapted to accompany the projection of a series of diapositive images or lantern slides--into electrical signals. This transducer is connected to a recording device 2 which can operate according to any principle, such as for example that of magnetic tapes, phonograph discs, or optical films.
The recording system also comprises an oscillator 3 delivering a carrier signal of any electrical frequency (Fp).
The oscillator 3 is modulated by a second oscillator 4 producing a modulating signal whose electrical frequency (Fm) is necessarily different from the carrier frequency (Fp). Thus, the signal issuing from the oscillator 4 modulates, that is, varies the phase, frequency or amplitude of the signal from the oscillator 3. This group of signals is applied to the input of the recording device 2 through switch means 5 whereby it is possible to apply only constant duration pulses of the modulated signal. The latter, which is mixed with the signals from the transducer, therefore forms the complex signal which is recorded by the recording device 2 on a support suitable for this operation such as, for example, a magnetic tape, a photograph disc, an optical film, or the like.
The frequencies employed by the oscillators 3 and 4 can have any values. However, they cannot be identical. By way of example, and in order to permit the reproduction by means of conventional reading or reproducing apparatuses, the carrier frequency Fp could be chosen to be 8,000 Hz. and the modulating frequency Fm to be 50 Hz. Thus, the modulation of Fp could be chosen to be one of amplitude by the frequency Fm. FIG. 2 shows a reading system for the signal recorded by the recording system shown in FIG. 1.
This system comprises a reading apparatus proper 6, such as a record player if the recording has been effected on a phonograph disc for example, a tape recorder if a magnetic tape has been used, etc. The output of the reading apparatus 6 is connected to a filter 7 whose resonance is tuned to the frequency of 8,000 Hz. in the chosen example.
This filter consists of an inductance coil S1 and a capacitor C1. It has a maximum impedance at its resonant frequency and is therefore capable of opposing the transmission to a loudspeaker 8 connected thereto, frequencies of value Fp, namely 8,000 Hz. in this example. Now, the filter 7 is short circuited by a switch 9 the action of which will be described hereinafter. The speaker 8 therefore receives all the recorded signals with elimination of no frequency and complete fidelity of the recording is therefore achieved.
Further, the output of the reading apparatus 6 is connected to a filter 10 whose resonant frequency is tuned to the frequency Fp (8,000 Hz.). This filter 10 consists of an inductance coil S2 and a capacitor C2 and is connected in such a manner that it has a minimum impedance at its resonant frequency and therefore only transmits a narrow band of frequencies centered on the frequency Fp to an amplifier 11 connected thereto. These signals are thus amplified at the output of the amplifier 11 and applied to a filter 12 also tuned to the frequency Fp, this filter consisting of an inductance coil S3 and a capacitor C3, whereby to improve the selectivity of the system, that is the capacity to separate the frequencies applied to the filter 10. The signals of frequency Fp available on the filter 12 are received by a winding 13 and then transmitted to an amplitude detector 14 whose function is to eliminate the carrier frequency Fp and make the modulating signal Fm appear. This signal of frequency Fm, namely 50 Hz. in the presently described example, is then applied to another amplifier 15 which is connected to a filter 16 consisting of an inductance coil S4 and a capacitor C4. This filter 16 is tuned to the value of the frequency Fm. The signal of frequency Fm available at the filter 16 is received by a winding 17, coupled to the winding S4, and thereafter rectified by a diode 18, that is converted into a DC voltage which is again amplified by an amplifier 19 and applied to an electromagnet 20 which it is capable of energizing.
The electromagnet 20 actuates the switch 9 and another switch 21. When closed by the action of the electromagnet 20, the switch 21 controls an image-changing device 22 of a projector (not shown), which is the desired function in the presently described example. When opened by the action of the electromagnet 20, the switch 9 opens the short circuit of the filter 7 and the latter then opposes the transmission to the speaker 8 of the signals which had initiated the control or actuation of the device 22. These signals are consequently not perceived by the audience.
This system operates in the following manner:
If a signal of frequency Fp is read by the reading or reproducing device, there are two possibilities:
1. This signal comes from a sound of the commentary and must not initiate the actuation of the image-changing device 22; it must therefore be perceived by the audience.
Being of suitable frequency, this signal is not stopped by the filter 10, is amplified by the amplifier 11 and available on the filter 12. It is received by the winding 13 and transmitted to the diode 14. But as it does not have the modulating frequency Fm, its detection does not result in a suitable signal capable of passing through the amplifier 15 and no signal appears on the filter 16 and nothing can be received by the winding 17. No voltage is applied to the diode 18 and no voltage is therefore transmitted to the amplifier 19 which cannot energize the electromagnet 20. The switch 21 remains open and does not actuate the changing device 22. The switch 9 remains closed and still short circuits the filter 7 and consequently the sound of frequency Fp can be reproduced by the speaker 8.
2 . This signal comes from a pulse of the oscillator 3 (FIG. 1) modulated by the oscillator 4 and must therefore actuate the changing device 22 without being perceived by the audience.
As this signal is of suitable frequency it is not stopped by the filter 10 and is amplified by the amplifier 11 and available on the filter 12. It is received by the winding 13 and transmitted to the diode 14. As this signal comprises the frequency Fm its detection results in a signal of frequency Fm at the input of the amplifier 15 and this amplified signal appears at the filter 16 and is received by the winding 17. The signal is rectified by the diode 18 and a DC voltage appears at the input of the amplifier 19. When amplified, this voltage is applied to the electromagnet 20 which it actuates. The switch 21 closes and actuates the changing device 22, the switch 9 opens and causes the filter 7 to operate and the latter opposes the transmission to the speaker 8 of this signal of frequency Fp. The signal consequently remains inaudible to the audience since it is not reproduced by the speaker.
The actuation of the changing device 22 therefore requires a double information, namely the reading of a frequency Fp and the modulation of this frequency by another frequency Fm. The application of either of these frequencies alone results in no reaction. The application of frequency Fp alone resumes the first possibility described hereinbefore and a signal having the frequency Fm alone cannot pass the filter 10.
It should be mentioned that the simultaneous application of two distinct frequencies, one of value Fp and the other of value Fm, cannot satisfy the complete detection. These frequencies must be in close relationship according to the type of detection employed. This relationship is a modulation of the amplitude of frequency Fp by the frequency Fm, which is the relationship chosen in the example shown in FIG. 2 (diode 14), a modulation of the frequency Fp by Fm, or a modulation of the phase of Fp by Fm.
It should also be noted that the frequency Fm cannot be reproduced by the speaker 8 since this frequency does not appear at the output of the reading apparatus 6. The appearance of frequency Fm essentially implies a detection of Fp appropriate to the modulating method employed when recording in accordance with the system shown in FIG. 1.
It will be understood that the reading system described hereinbefore employs a recording consisting of a complete audio spectrum having at certain intervals a pulse of frequency Fp modulated by a frequency Fm, these pulses resulting in the changing of diapositive images or lantern slides. The frequency Fp is therefore only eliminated from the audio spectrum perceived by the audience when a control pulse is produced. In practice, this spectrum can be considered as being fully transmitted.
However, it is possible to record several types of control pulses modulated with distinct frequencies, which serve in the reading system after filtering in particular filters, too obtain several control signals, these pulses for example starting up a second projector or lighting up the projecting room. These pulses can of course be modulated in different ways.
One embodiment of such a reading system is shown in FIG. 3. In this diagram, the reproducing channel and the filters and relay contacts have been omitted for reasons of clarity.
The control signals received in a reading device 30 are transmitted to a first filter of frequency Fp, namely filter 31. Its output signal is transmitted, detected and filtered in three separate channels, 32, 33 and 34 (Fm1, Fm2, Fm3) controlling relays 35, 36 and 37 respectively, the latter serving to control a first projector, start a second projector when the first has used up a batch of diapositive images or lantern slides and light up the room at the end of the commentary.
It will be observed that the carrier frequency is modulated in amplitude by the frequency Fm1 and modulated in frequency by the frequencies Fm2 and Fm3. A discriminator 29 detects the latter frequencies.
With reference to FIG. 4, which has been given only by way of example, a few properties of an electromagnetic relay will now be recalled.
A relay R is fed by a battery B through a potentiometer P. The potentiometer varies the intensity of the energization current of the relay R. It is observed that the intensity required for holding the relay exceeds the intensity, when the energization is no longer sufficient, at which the relay is released. Consequently, the relay can be operated by energizing it with a pulse of given current density (point x). It is observed that the relay remains energized with a much smaller intensity (point y).
This feature of relay operation can be employed in the method according to the invention. Indeed, according to a particular feature of the invention, the purpose of which is to render the control pulses as inaudible as possible when reproducing, the amplitude of each of these pulses follows a decreasing law. The control relay 22 (FIG. 2) is energized at the start of the pulse and maintained in this position by the rest of the pulse until the amplitude at which the energization can no longer be maintained is reached.
It will be understood that, in this way, the pulse, while it has an action identical to that of pulses of constant amplitude, is less perceptible to the audience, on one hand because the pulse appears to be of shorter duration to the listener, and, on the other hand, because as the ear is very sensitive to sudden variations in the perceived spectrum, one of the variations has become very regular, namely the variations which puts a stop to the pulse.
One embodiment, by which the invention is not intended to be limited, of a device for obtaining control pulses having a decreasing law is shown in FIG. 5. This device is no other than a special form of the switch 5 shown in FIG. 1 and comprises a capacitor 38, one terminal of which is earthed and the other connected to the junction point of two resistors 39 and 40. A pushbutton 41 is connected in parallel with the capacitor 38. The resistor 40 is connected in series with a polarization battery 42 whose positive terminal is earthed. The resistor 39 is connected to the input 43 of the device (connected to the output of the oscillator 3 shown in FIG. 1) and to the grid of a triode 44 connected as an amplifier. The anode of the triode is connected in series with an anode resistor 45 and a battery 46, and to the output terminal 47 of the switch, which is connected to the recording device 2 (FIG. 1).
While the pushbutton 41 is open, the triode 44 is turned off by the polarization voltage supplied by the battery 42, the capacitor 38 being charged. The signal from the oscillator 3 (FIG. 1) therefore cannot pass through the triode and reach the recording device 2.
When it is desired to record a control pulse, that is, change from one diapositive image or lantern slide to another, the pushbutton 41 is actuated in such a manner that the capacitor 38 is discharged instantaneously. The triode can therefore amplify the signal applied to its grid, the latter having the potential of the earth. However, the capacitor is charged progressively so that the triode is polarized progressively until turned off. The output pulse therefore follows a decreasing law.
Note that a recording effected in accordance with the method of the invention can be read or reproduced if desired with a reading or reproducing system adapted to reproduce recordings made in accordance with the conventional method described hereinabove.
However, in this case, one condition must be satisfied when recording. The electrical signal must be slightly attenuated at the carrier frequency Fp so that a sound, normally emitted during the commentary at this frequency and having a sufficiently high amplitude level, does not accidentally cause the image-changing relay to respond. Further, the pulses must be recorded by means of the device described with reference to FIG. 5 so as to render them as little audible as possible. The image-changing relay is then energized by the start of the pulse and will remain energized practically until its disappearance. The modulation frequency Fm in this case is not detected.
However, it will be observed that the level of the control pulse can be lower in this case, and consequently less audible, if its modulation is effected in amplitude for a given sensitivity of the control relay. Indeed, as the modulation frequency is not perceptible in the speaker of the conventional system since no detection is effected, it is however superimposed on the DC current resulting from the detection of the signal Fp of the control pulse. The pulse of the current which actuates the control relay is an undulating current whose crests are higher than in the case where unmodulated pulses would be recorded (the case of a conventional recording method). Consequently, the recording according to the invention can be read or reproduced in conventional reproducing systems, it being possible for the control pulses to have a much higher amplitude at the frequency Fp than they have in recordings made in accordance with the conventional recording method. The pulses will therefore be less audible.
An example, by which the invention is not intended to be limited, will now be given of a recording made by the method according to the invention. This recording can be reproduced with the conventional reproducing system and with the system according to the invention, the control part of which is shown in FIG. 3.
The recording made with a system including the switch shown in FIG. 5 is made under the following conditions:
The sound channel employed has a range of 20-50,000 Hz. The images are changed by control pulses obtained from a signal of 7,000 Hz. which is 100 percent amplitude modulated by a frequency of 50 Hz. The pulses exhibit a decreasing amplitude. Changing from the first projector to the second projector, after the batch of diapositive images or lantern slides of the second projector has been used up, is effected by means of a control pulse of 7,000 Hz. which is frequency-modulated by a signal of 100 Hz. and amplitude modulated at 50 Hz. A control pulse of 7,000 Hz. frequency-modulated by a signal of 400 Hz. is recorded for automatically lighting up the projecting room.
During the reproduction in a reading or reproducing system designed in accordance with the conventional method, the control pulses of 7,000 Hz. modulated with a signal of 50 Hz., change the images, the control relay of the image-changing device being energized at the start of the pulse by the maximum amplitude and maintained in its energized position by the rest of this control pulse of decreasing amplitude. The pulses of 7,000 Hz. frequency-modulated at 100 Hz. and at 400 Hz. are ineffective since, as they have not been modulated in amplitude, their amplitude is insufficient to actuate the relay.
It should be mentioned that the frequency of 7,000 Hz. cannot reach the audience since a filter is provided in the reproduction channel.
During the reproduction in a system according to FIG. 3, the pulses control respectively:
at 7,000 Hz. with amplitude modulation 50 Hz. (Fm1), the relay 1; image changing,
at 7,000 Hz. with frequency modulation (Fm2) the relay 2; the connection and starting up of the second projector, the first projector being put out of operation,
at 7,000 Hz. with frequency modulation at 400 Hz. (Fm3)--the relay 3 alone is energized and the lights in the projecting room are turned on.
Although specific embodiments of the invention have been described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claims.