EP0744105B1 - Procede et systeme de brouillage et de desembrouillage d'un signal acoustique - Google Patents
Procede et systeme de brouillage et de desembrouillage d'un signal acoustique Download PDFInfo
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- EP0744105B1 EP0744105B1 EP94931915A EP94931915A EP0744105B1 EP 0744105 B1 EP0744105 B1 EP 0744105B1 EP 94931915 A EP94931915 A EP 94931915A EP 94931915 A EP94931915 A EP 94931915A EP 0744105 B1 EP0744105 B1 EP 0744105B1
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- signal
- frequency
- modulation
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- sideband
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
- H04K1/00—Secret communication
- H04K1/04—Secret communication by frequency scrambling, i.e. by transposing or inverting parts of the frequency band or by inverting the whole band
Definitions
- the present invention relates to a method and system for scrambling and descrambling audio signals.
- FIG 1 is a block diagram of the key elements of a descrambler circuit as described in US patent No. 4,636,853 ('853) of Forbes.
- the Forbes '853 descrambler 10 has a scrambled audio input 34 which is connected to an all pass phase shifter 20 containing a 0 degree output 38 and a 90 degrees output 39.
- the scrambled audio signal has an offset frequency 36 F 1 -F 2 as shown in Figure 2A. This shows the scrambled audio offset by an offset frequency determined by the scrambling process.
- the phase shifted outputs are connected to a first input of linear modulators 21 and 27.
- a frequency generator 22 generates a square wave frequency (F 1 ) which is fed to band pass filter 24 to remove any harmonics, thus producing a pure sine wave.
- This F 1 sine wave is connected to a 0 degree and 90 degree phase shifter 25.
- the outputs of phase shifter 25 are in turn connected to second inputs of linear modulators 21 and 27 respectively.
- the outputs of the first and second linear modulators are added in summer 28 to produce signal 37.
- This output signal 37 is connected to a first input of a second mixer 30 via high pass filter 29 which passes only F 1 and the upper sideband as shown in Figure 2B.
- a second square wave frequency generator 23 generates a signal F 2 as shown Figures 1 and 2B.
- This square wave is filtered by band pass filter 26 to remove any harmonics to produce a pure sine wave signal.
- This pure sine wave signal is connected to a second input of third mixer 30.
- the output of the third mixer 30 is connected to a low pass filter 31 to produce a descrambled output signal 35.
- the second spectral diagram in Figure 2B shows the input to the 3rd mixer 30.
- the frequency F 1 here represents the residual carrier feed through from mixers 21 and 27.
- Figure 2C shows the relationship of a carrier F 2 to F 1 in Figure 2B and the scrambled audio signal shown in Figure 2A.
- Figure 2D shows the relationship of the spectral characteristics of the descrambled signal 35 and the residual difference frequency (F 1 -F 2 ) component to the spectral characteristics of the signals in Figures 2A to 2C.
- Figure 3 shows the scrambled audio input of the Quan prior art descrambler 11. This shows the scrambled audio 30 offset by an offset frequency determined by the original scrambling process.
- the scrambled audio input signal 40 is connected to an all pass shifter 41 which provides 0 degree and 90 degree phase shifted outputs 42 and 43 to first inputs of first and second mixers 44 and 45.
- Carrier frequency generator 46 generates a sine wave signal F c 47 with a frequency of 1 Khz or 2-3 khz.
- the carrier frequency 47 is filtered by a low pass filter 48 to remove any harmonics to produce a pure sine wave 49.
- This pure sine wave signal 49 is connected to an all pass phase shifter 50 to produce 0 degree and 90 degree signals 51 and 52 which in turn are connected to second inputs of mixers 44 and 45.
- the outputs of mixers 44 and 45, signals 53 and 54 are connected to summer 55 to produce descrambled output 56.
- Figure 4B shows the relationship of the in band descrambling carrier F c to the scrambled audio signal.
- Figure 4C shows the descrambled audio spectrum with the residual carrier F c that is typically -60 db below the descrambled audio program, but is still audible during silent passages of the audio program.
- US-A-4,636,853 describes a system for descrambling a scrambled frequency translated audio information signal by generating a modulation carrier signal at a frequency lying outside the original frequency spectral range of an original audio signal of about 50 Hz to about 15 Khz, the descrambling system comprising:
- the known descrambling/scrambling system has noise problems in that white thermal or shot noise of circuit components degrades the signal to noise (SNR) of the system. There is also in-band audible carrier whistle.
- SNR signal to noise
- a descrambling system of the type defined is characterised in that, to produce a descrambled audio signal containing substantially no audible whistle components said first modulated signal is a first double sideband signal having said first modulation frequency, a first upper sideband signal and a first lower sideband signal; and said first filtering means filters out said first modulation frequency, all its harmonics, and said first upper sideband signal from said first double sideband signal and passes said first lower sideband signal;
- each of said first and second modulation carrier signals is a square wave signal
- each of said first and second modulating means is a square wave modulator arranged to modulate its respective incoming signal with the respective first or second square wave modulation carrier signal
- the present invention also extends to a system for scrambling an original audio signal of about 50 Hz to about 15 KHz, the scrambling system comprising:
- each of said first and second modulation carrier signals is a square wave signal
- each of said first and second modulating means is a square wave modulator arranged to modulate its respective incoming signal with the respective first or second square wave modulation carrier signal
- square wave modulators are utilised which are low noise.
- Embodiments of scramblers and descramblers of the invention utilising square wave modulators have been found to eliminate in band audible whistle and to eliminate the need to adjust the mixers for minimum in band carrier whistle. As the SNR has been improved, the need for noise reduction circuits has been eliminated.
- the square wave modulators may be switching type mixer circuits which are of a lower cost and reduce white noise as compared to linear mixer circuits.
- Embodiments of scramblers and descramblers of the present invention also eliminate the use of 0 degree and 90 degree phase shift circuits, eliminate the use of quadrature mixer circuits, and eliminate the need for band pass filters or low pass filters for the modulation carrier.
- said switch type low noise modulators may comprise a differential pair balanced multiplier type modulator.
- said switch type low noise modulators may comprise MC1496 modulators, or an analog switch coupled to inverse polarities of an incoming signal.
- said first filtering means comprises an elliptical filter containing at least seven poles.
- said first filtering means comprises an active filter having nine poles with general impedance convertors.
- said second filtering means comprises a filter with seven or more poles.
- the present invention also extends to a method of descrambling scrambled frequency spectrum translated audio information signals by generating a modulation carrier signal at a frequency lying outside the original frequency spectral range of an original audio signal of about 50 Hz to about 15 Khz, the method comprising the steps of:
- the method further comprises the steps of generating each of said first and second modulation carrier signals as a square wave signal;
- said first modulation carrier signal has a frequency of at least 19 Khz.
- said second modulation carrier signal has a frequency less than said first modulation frequency by at least 500 Hz.
- said second modulation carrier signal has a frequency about 2.6 Khz less than said first modulation frequency.
- a method of scrambling an original audio signal of about 50 Hz to about 15 Khz comprising the steps of:
- the method further comprises the steps of generating each of said first and second modulation carrier signals as a square wave signal, and modulating each of said original audio signal and said first lower sideband signal with the respective first or second square wave modulation carrier signal.
- said first modulation carrier signal has a frequency of at least 16.4 Khz.
- said modulation carrier signal has a frequency at least 50 Hz greater than said first modulation carrier frequency.
- said second modulation carrier signal has a frequency of about 19 Khz.
- the frequency of said second modulation carrier signal is pseudo randomly varied.
- Figure 5 shows a block diagram and Figure 6 shows a spectral diagram of a descrambler of a preferred embodiment of the invention.
- Figure 6A shows the spectral characteristic of the scrambled audio input of the preferred embodiment. This shows the scrambled audio offset by an offset frequency determined by the scrambling process.
- Figure 6B shows the relationship of the first mixer's carrier and the output of the first mixer. Both the upper and lower sidebands and the residual carrier F A plus the harmonics of all of these are at the first mixer's output.
- Figure 6C shows the filter characteristics of the first low pass filter (LPF) following the first mixer's output. This first LPF filters out the residual carrier and its upper sideband harmonics.
- Figure 6D shows the spectral characteristic of the output of the first LPF following the first mixer's output.
- LPF low pass filter
- Figure 6E shows the relationship of the second carrier to the output of the first LPF to form the last descrambling step.
- Figure 6F shows the relationship of the descrambled audio that has passed through a 2nd LPF with a 12 khz cut-off to filter out F B and its upper sideband above F B with the absence of whistle frequency component (F A -F B ).
- the (F A -F B ) whistle frequency component is typically equal or less than -85 db in the descrambled audio.
- F A is about 19 Khz and F B is about 16.4 Khz.
- Minimal carrier leakage and scrambled audio leakage with lower shot noise is achieved by using a double throw single pole analog switch such as the 74 HCT 4053 or its equivalent i.e. MC1496 switch type mixer with a carrier input equal to or more than 350 mv p-p.
- the preferred embodiment uses a low pass filter (LPF) after the first mixer which is to reject out a residual carrier from the first mixer and remove all sidebands related to harmonics of the carrier and the harmonics of the carrier. If this is not done, harmonics of the whistle frequency (3F A - 3F B ), (5F A -5F B ) and etc. will appear at the descrambling output in an audible manner.
- This first LPF is generally a 7 pole or more elliptical filter with at least one zero tune to notch out the first mixer's carrier frequency, F A .
- a 9 pole active filter with general impedance convertors is the best choice for a stable and accurate filter.
- the 3 db cut off of the first low pass filter is about 17 Khz with at least 40 db attenuation at 19 Khz.
- the descrambling apparatus 12 has a scrambled audio signal input 60 and performs the descrambling process.
- the scrambled audio 60 is inputted into a first input of a first mixer 63.
- the second input of this first mixer is a first carrier signal F A generated by frequency generator A 1 61 which is approximately 19 Khz.
- the output first mixer 63 contains carrier feed through of F A all its sideband components and the harmonics.
- the output of mixer 63 is fed to a low pass filter 65 which filters out the first carrier, the upper sideband and all of the harmonics from signal 60.
- the output of low pass filter 65, signal 66 is fed into a first input of a second mixer 66.
- the second input of this second mixer is a second carrier signal F B generated by frequency generator B, 62 which can be 16.4 Khz or 16.4 Khz +/- 100 Hz shifted pseudo randomly for security reasons. See U.S. Patent 5,095,279 for a further explanation of this security process.
- the output of second mixer 70 contains the baseband descrambled audio, residual second carrier and upper sideband components above F B 's frequency.
- the second low pass filter 71 with a cut-off frequency of approximately 12 Khz removes everything above 12 Khz, but passes the descrambled audio to the output line 23.
- the mixers utilize a switch type low shot or thermal noise modulator as described in Figure 7.
- the operation of this mixer will be described relative to the first mixer.
- the second mixer operates on the same principle. Scrambled audio 60 is fed into the + input of unity gain amplifier 73.
- the output of amplifier 73 is fed on line V IN 74 to one input of a double pole single throw analog switcher 32.
- the output of 73 is also fed to the input of unity gain inversion amplifier consisting of R2a, R2b, and amplifier 65.
- the output of amplifier 65 is -V IN 75 which is fed to a second input of the switcher 32.
- First carrier frequency F A is fed into the switching control input of the double pole, single throw switcher 32.
- the double pole, single throw switcher used is one-third of an 74HCT4053 or its equivalent and is fed to amplifier A220.
- A220 is the mixer output.
- the DC zero signal voltage of the two inputs of switch 32 V IN and -V IN must be exactly the same, i.e. Ov.
- the inversion amplifier R2a, R2b, 65 must be -1 unity gain to have minimum scrambled audio in V IN feed through.
- Figure 13A shows a conventional RLC low pass filter with zeros for the descrambler's first low pass filter.
- the inductors L 1 through L 3 are rather large, 2 milli-henries to 20 milli-henries, to achieve a low cost. These lower cost inductors suffer from a just adequate Q at audio frequencies. Much more expensive inductors with higher Q's will provide better low pass filtering, but will be beyond the budget of a low cost descrambling system.
- Figure 13B shows an active 9 pole elliptic low pass filter that is not as sensitive to parts tolerance as many other active filters. This is important since F A , the first carrier frequency must be filtered out by at least -40 db attenuation.
- Figure 13B is a general impedance converter (GIC) active low pass filter that was found to provide very high performance in filtering at low cost.
- the capacitors can be inexpensive 5% mylar film capacitors.
- the resistors are inexpensive 1% resistors and the operational amplifiers can be common type such as TL082, NE5532 etc.
- Figure 13C shows an example of the second filter as an active 7 pole low pass filter.
- Amplifiers A1000, A2000 and A3000 can be simple voltage followers of common operational amplifiers or single transistor emitter followers.
- the second filter in the descrambler can be any low pass filter, passive or active with sufficient stop band attenuation to provide a descrambled audio signal without measurable artifacts such as second carrier tone its upper sidebands and/or audible artifacts.
- FIGS 8 to 11 show various implementations of the invention.
- FIG. 11 is a block diagram and Figure 12 is a series of spectral diagrams of a preferred embodiment of a scrambler.
- An audio signal with a spectral response of about 30 Hz to 15 Khz 91 is fed into a low pass filter 20 to eliminate any unwanted signals beyond 15 Khz.
- the output 93 of low pass filter 20 is connected to 0 degree and 90 degree all pass phase shifters 94 and 95.
- the outputs of phase shifters 94 and 95 are in turn connected to first inputs of switch type low noise modulators 96 and 97.
- Signal generator 98 generates a square wave signal at approximately 16.4 Khz with 0° and 90° outputs which are connected to second inputs of modulators 96 and 97. The outputs of modulators 96 and 97 are summed to produce signal 103, a quadrature modulated signal resulting in a residual 16.4 Khz carrier with a lower sideband.
- Figure 12 shows the relationship of the quadrature modulated audio components to the original audio signal 91.
- This quadrature modulated signal is fed through low pass filter 104 as signal 105 and is essentially the same filter as the first filter of the descrambler described above.
- This signal is connected to a first input of a third modulator 106.
- Modulator 106 is a switch type low thermal or shot noise modulator as described above and as shown in Figure 7.
- a second carrier frequency is generated by a square wave oscillator 99 generating a frequency of approximately 19 Khz as shown in Figure 12E.
- the output of modulator 106 contains a 16 Khz carrier and upper and lower sidebands. This signal is filtered by low pass filter 107 to produce a scrambled audio signal with an offset of approximately 2.6 Khz.
- the low pass filters following the first quadrature mixer the first mixer of both the scrambler and descrambler respectively should be very nearly identical in group delay responses (transient responses). If the transient response characteristics of the low pass filters in the scrambler are different from the transient characteristics of the descrambler, the step changes of the 16.4 Khz carrier has to be slowed down to achieve minimal descrambling artifacts.
- the first low pass filter in the descrambler has the same characteristics as filter 104 in the scrambler of Figure 11.
- the second low pass filter in the descrambler should have the same characteristics of filter 107 of the scrambler of Figure 11. This permits the step shifting spectrum of the scrambler to be tracked quickly in the descrambler without artifacts caused by time delay skews between scrambler and descrambler tracking the 16 Khz stepped deviations.
- all carriers for all mixers in this invention for descramblers and scramblers are square wave signals for minimum artifacts.
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Claims (22)
- Système pour désembrouiller un signal d'information audio transposé en fréquence et brouillé en générant un signal de porteuse de modulation à une fréquence se situant à l'extérieur de la gamme spectrale de fréquence originale d'un signal audio original d'environ 50 Hz à environ 15 kHz, le système de désembrouillage comprenant :un premier générateur de signal (61) pour générer un premier signal de porteuse de modulation (FA) ayant une fréquence supérieure à la fréquence la plus haute dans le signal audio original ;des premiers moyens de modulation (63) pour moduler ledit signal audio brouillé avec ledit premier signal de porteuse de modulation afin de produire un premier signal modulé ayant ladite première fréquence de modulation ;des premiers moyens de filtrage (65) pour rejeter un premier signal à bande latérale haute dudit premier signal modulé afin de produire un premier signal filtré ;un second générateur de signal (62) pour générer un second signal de porteuse de modulation (FB) ayant une fréquence inférieure à ladite première fréquence de modulation ;des seconds moyens de modulation (67) pour moduler ledit premier signal filtré avec ledit second signal de porteuse de modulation afin de produire un second signal modulé ayant ladite seconde fréquence de modulation ; etdes seconds moyens de filtrage (71) destinés à laisser passer un second signal à bande latérale provenant dudit second signal modulé afin de produire un signal audio désembrouillé ;le système de désembrouillage étant caractérisé en ce que, pour produire un signal audio désembrouillé ne contenant sensiblement aucune composante de sifflement audible, ledit premier signal modulé est un premier signal à bande latérale double ayant ladite première fréquence de modulation, un premier signal à bande latérale haute et un premier signal à bande latérale basse ; et lesdits premiers moyens de filtrage (65) éliminent par filtrage ladite première fréquence de modulation, tous ses harmoniques, et ledit premier signal à bande latérale haute dudit premier signal à bande latérale double et laissent passer ledit premier signal à bande latérale basse ;et en ce que ledit second signal modulé est un second signal à bande latérale double ayant ladite seconde fréquence de modulation, un second signal à bande latérale haute et un second signal à bande latérale basse ; et en ce que lesdits seconds moyens de filtrage (71) filtrent ledit second signal à bande latérale double et ne laissent passer que ledit second signal à bande latérale basse pour produire ledit signal audio désembrouillé.
- Système de désembrouillage selon la revendication 1, dans lequel chacun desdits premier et second signaux de porteuses de modulation (FA ; FB) est un signal en onde carrée, et chacun desdits premier et second moyens de modulation (63, 67) est un modulateur à onde carrée conçu pour moduler son signal d'entrée respectif avec le premier ou le second signal de porteuse de modulation en onde carrée respectif.
- Système pour brouiller un signal audio original d'environ 50 Hz à environ 15 kHz, le système de brouillage comprenant :un premier générateur de signal (98) pour générer un premier signal de porteuse de modulation (FF) ayant une fréquence supérieure à la fréquence la plus haute dans le signal audio original ;des premiers moyens de modulation (96, 97) pour moduler le premier signal audio original avec ledit premier signal de porteuse de modulation afin de produire un premier signal modulé ayant ladite première fréquence de modulation ;des premiers moyens de filtrage (104) pour rejeter un premier signal à bande latérale haute dudit premier signal de modulation afin de produire un premier signal filtré ;un second générateur de signal (99) pour générer un second signal de porteuse de modulation (FA) ayant une fréquence supérieure à ladite première fréquence de modulation ;des seconds moyens de modulation (106) pour moduler le premier signal filtré avec ledit second signal de porteuse de modulation afin de produire un second signal modulé ayant ladite seconde fréquence de modulation ; etdes seconds moyens de filtrage (107) pour laisser passer un second signal à bande latérale provenant dudit second signal de modulation afin de produire un signal audio brouillé ;le système de brouillage étant caractérisé en ce que, pour produire un système audio brouillé ayant un plus faible niveau de bruit, ledit premier signal modulé est un premier signal à bande latérale en quadrature ayant une première fréquence de modulation, un premier signal à bande latérale haute et un premier signal à bande latérale basse, et en ce que lesdits premiers moyens de filtrage (104) filtrent la première fréquence de modulation et ses harmoniques, et ledit signal à bande latérale haute et ses harmoniques dudit premier signal à bande latérale en quadrature et laissent passer ledit premier signal à bande latérale basse ;et en ce que ledit second signal modulé est un second signal à bande latérale double ayant ladite seconde fréquence de modulation, un second signal à bande latérale haute et un second signal à bande latérale basse ; et lesdits seconds moyens de filtrage (107) filtrent ledit second signal à bande latérale double et ne laissent passer que ledit second signal à bande latérale basse pour produire ledit signal audio brouillé.
- Système de brouillage selon la revendication 3, dans lequel chacun desdits premier et second signaux de porteuses de modulation (FF ; FA) est un signal en onde carrée, et chacun desdits premier et second moyens de modulation (96, 97 ; 106) est un modulateur à onde carrée conçu pour moduler son signal d'entrée respectif avec le premier ou le second signal de porteuse de modulation en onde carrée.
- Système selon l'une quelconque des revendications précédentes, dans lequel lesdits premier et/ou seconds moyens de modulation (63, 67 ; 96, 97, 106) comprennent des modulateurs à faible bruit, du type commutateur.
- Système selon la revendication 5, dans lequel lesdits premier et seconds moyens modulateurs (63, 67) à faible bruit, du type commutateur comprennent des modulateurs du type MC 1496.
- Système selon la revendication 5, dans lequel l'un desdits modulateurs à faible bruit du type commutateur (63, 106) comprend un commutateur analogique couplé de façon à inverser les polarités du signal ou des signaux entrant(s).
- Système selon la revendication 5, dans lequel lesdits modulateurs à faible bruit du type commutateur (106) comprennent un modulateur du type multiplieur équilibré à paire différentielle.
- Système selon l'une quelconque des revendications précédentes, dans lequel lesdits premiers moyens de filtrage (65 ; 104) comprennent un filtre elliptique contenant au moins sept pôles.
- Système selon la revendication 9, dans lequel lesdits premiers moyens de filtrage (65 ; 104) comprennent un filtre actif ayant neuf pôles à convertisseurs d'impédance généraux.
- Système selon l'une quelconque des revendications précédentes, dans lequel lesdits seconds moyens de filtrage (71 ; 107) comprennent un filtre à sept pôles ou davantage.
- Procédé de désembrouillage de signaux d'informations audio brouillés à spectre de fréquence transposé en générant un signal de porteuse de modulation à une fréquence se situant à l'extérieur de la gamme spectrale de fréquence originale d'un signal audio original d'environ 50 Hz à environ 15 kHz, le procédé comprenant les étapes qui consistent :à générer un premier signal de porteuse de modulation (FA) ayant une fréquence supérieure à la fréquence la plus haute dans le signal audio original ;à moduler ledit signal audio brouillé avec ledit premier signal de porteuse de modulation afin de produire un premier signal modulé ayant ladite première fréquence de modulation ;à filtrer ledit premier signal modulé pour rejeter un premier signal latéral à bande latérale haute et produire un premier signal filtré ;à générer un second signal de porteuse de modulation (FB) ayant une fréquence inférieure à ladite première fréquence de modulation ;à moduler ledit premier signal filtré avec ledit second signal de porteuse de modulation afin de produire un second signal modulé ayant ladite seconde fréquence de modulation ; età filtrer ledit second signal modulé pour laisser passer un second signal à bande latérale afin de produire un signal audio désembrouillé ;et en ce que ledit second signal modulé est un second signal à bande latérale double ayant ladite seconde fréquence de modulation, un second signal à bande latérale haute et un second signal à bande latérale basse, et ladite seconde étape de filtrage consiste à filtrer dudit second signal modulé ladite seconde fréquence de modulation, et ledit second signal à bande latérale haute et à ne laisser passer que ledit second signal à bande latérale basse pour produire ledit signal audio désembrouillé.
- Procédé selon la revendication 12, comprenant en outre les étapes consistant à générer chacun desdits premier et second signaux de porteuses de modulation (FA ; FB) sous la forme d'un signal en onde carrée ; età moduler chacun dudit signal audio brouillé et dudit premier signal à bande latérale basse avec le premier ou le second signal de porteuse de modulation en onde carrée respectif.
- Procédé selon la revendication 12 ou 13, dans lequel ledit premier signal de porteuse de modulation (FA) a une fréquence d'au moins 19 kHz.
- Procédé selon la revendication 10 ou 11, dans lequel ledit second signal de porteuse de modulation (FB) a une fréquence inférieure d'au moins 500 Hz à ladite première fréquence de modulation.
- Procédé selon la revendication 15, dans lequel ledit second signal de porteuse de modulation a une fréquence inférieure d'environ 2,6 kHz à ladite première fréquence de modulation.
- Procédé de brouillage d'un signal audio original d'environ 50 Hz à environ 15 kHz, le procédé comprenant les étapes qui consistent :à générer un premier signal de porteuse de modulation (FF) ayant une fréquence supérieure à la fréquence la plus haute dans le signal audio original ;à moduler ledit signal audio original avec ledit premier signal de porteuse de modulation afin de produire un premier signal modulé ayant ladite première fréquence de modulation ;à filtrer ledit premier signal modulé afin de rejeter un premier signal à bande latérale haute et de produire un premier signal filtré ;à générer un second signal de porteuse de modulation (FA) ayant une fréquence plus haute que ladite première fréquence de modulation ;à moduler ledit premier signal filtré avec ledit second signal de porteuse de modulation afin de produire un second signal modulé ayant ladite seconde fréquence de modulation ; età filtrer ledit second signal modulé pour laisser passer un second signal à bande latérale afin de produire un signal audio brouillé ;et ledit second signal modulé est un second signal à bande latérale double ayant une seconde fréquence de modulation, un second signal à bande latérale haute et un second signal à bande latérale basse, et ladite seconde étape de filtrage consiste à filtrer dudit second signal modulé ladite seconde fréquence de modulation et ledit second signal à bande latérale haute, et à laisser passer ledit second signal à bande latérale basse pour produire ledit signal audio brouillé.
- Procédé selon la revendication 17, comprenant en outre les étapes consistant à produire chacun desdits premier et second signaux de porteuses de modulation (FF, FA) sous la forme d'un signal en onde carrée, et à moduler chacun dudit signal audio original et dudit premier signal à bande latérale basse avec le premier ou le second signal de porteuse de modulation en onde carrée.
- Procédé selon la revendication 17 ou 18, dans lequel ledit premier signal de porteuse de modulation (FF) a une fréquence d'au moins 16,4 kHz.
- Procédé selon l'une quelconque des revendications 17 à 19, dans lequel ledit signal de porteuse de modulation (FA) a une fréquence supérieure d'au moins 50 Hz à ladite première fréquence de porteuse de modulation.
- Procédé selon la revendication 20, dans lequel ledit second signal de porteuse de modulation (FA) a une fréquence d'environ 19 kHz.
- Procédé selon l'une quelconque des revendications 12 à 21, dans lequel la fréquence dudit second signal de porteuse de modulation (FB, FA) est amené à varier de façon pseudo-aléatoire.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
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US14506693A | 1993-10-26 | 1993-10-26 | |
US145066 | 1993-12-14 | ||
PCT/US1994/011891 WO1995012922A2 (fr) | 1993-10-26 | 1994-10-18 | Procede et appareil de brouillage et de desembrouillage economiques de signaux basse frequence |
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Publication Number | Publication Date |
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EP0744105A1 EP0744105A1 (fr) | 1996-11-27 |
EP0744105B1 true EP0744105B1 (fr) | 1998-12-23 |
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Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP94931915A Expired - Lifetime EP0744105B1 (fr) | 1993-10-26 | 1994-10-18 | Procede et systeme de brouillage et de desembrouillage d'un signal acoustique |
Country Status (14)
Country | Link |
---|---|
EP (1) | EP0744105B1 (fr) |
JP (1) | JP3150700B2 (fr) |
KR (1) | KR100249656B1 (fr) |
AT (1) | ATE175063T1 (fr) |
AU (1) | AU695981B2 (fr) |
CA (1) | CA2181691C (fr) |
DE (1) | DE69415555T2 (fr) |
DK (1) | DK0744105T3 (fr) |
ES (1) | ES2125494T3 (fr) |
HK (1) | HK1013747A1 (fr) |
MY (1) | MY111488A (fr) |
NZ (1) | NZ275269A (fr) |
TW (1) | TW311307B (fr) |
WO (1) | WO1995012922A2 (fr) |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4636853A (en) * | 1983-12-21 | 1987-01-13 | Zenith Electronics Corporation | Dynamic audio scrambling system |
US5058159A (en) * | 1989-06-15 | 1991-10-15 | Macrovision Corporation | Method and system for scrambling and descrambling audio information signals |
US5159631A (en) * | 1990-04-26 | 1992-10-27 | Macrovision Corporation | Audio scrambling system using in-band carrier |
-
1994
- 1994-10-18 JP JP51324395A patent/JP3150700B2/ja not_active Expired - Lifetime
- 1994-10-18 AT AT94931915T patent/ATE175063T1/de not_active IP Right Cessation
- 1994-10-18 DE DE69415555T patent/DE69415555T2/de not_active Expired - Fee Related
- 1994-10-18 DK DK94931915T patent/DK0744105T3/da active
- 1994-10-18 KR KR1019960703240A patent/KR100249656B1/ko not_active IP Right Cessation
- 1994-10-18 CA CA002181691A patent/CA2181691C/fr not_active Expired - Fee Related
- 1994-10-18 AU AU80828/94A patent/AU695981B2/en not_active Ceased
- 1994-10-18 NZ NZ275269A patent/NZ275269A/en unknown
- 1994-10-18 EP EP94931915A patent/EP0744105B1/fr not_active Expired - Lifetime
- 1994-10-18 WO PCT/US1994/011891 patent/WO1995012922A2/fr active IP Right Grant
- 1994-10-18 ES ES94931915T patent/ES2125494T3/es not_active Expired - Lifetime
- 1994-10-25 MY MYPI94002827A patent/MY111488A/en unknown
- 1994-12-02 TW TW083111250A patent/TW311307B/zh not_active IP Right Cessation
-
1998
- 1998-12-23 HK HK98114981A patent/HK1013747A1/xx not_active IP Right Cessation
Also Published As
Publication number | Publication date |
---|---|
ES2125494T3 (es) | 1999-03-01 |
CA2181691C (fr) | 2000-10-17 |
JPH10500259A (ja) | 1998-01-06 |
NZ275269A (en) | 1998-08-26 |
TW311307B (fr) | 1997-07-21 |
DE69415555D1 (de) | 1999-02-04 |
JP3150700B2 (ja) | 2001-03-26 |
MY111488A (en) | 2000-06-30 |
DE69415555T2 (de) | 1999-05-12 |
DK0744105T3 (da) | 1999-08-23 |
AU695981B2 (en) | 1998-08-27 |
KR100249656B1 (ko) | 2000-03-15 |
AU8082894A (en) | 1995-05-23 |
ATE175063T1 (de) | 1999-01-15 |
HK1013747A1 (en) | 1999-09-03 |
CA2181691A1 (fr) | 1995-05-11 |
WO1995012922A2 (fr) | 1995-05-11 |
EP0744105A1 (fr) | 1996-11-27 |
WO1995012922A3 (fr) | 1995-07-13 |
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