JPH10500259A - Low cost audio scrambling and descrambling method and apparatus - Google Patents

Abstract

Audio signals are descrambled by double sideband modulating the scrambled audio signal with a modulation carrier having a carrier frequency slightly above the highest audio signal present in the scrambled audio. This produces a double sideband signal that is passed through a low pass filter which in turn is modulated by a second carrier frequency lower than the first carrier signal by equal to the offset spectrum of the original scrambled signal. The first low pass filter nulls out any residual carrier from the first modulator that results form the intermodulation of the two modulation frequencies that would be audible at its descrambler output. The modulators used are low noise switch type modulators that improve the signal to noise ratio in the descrambled signal over the previously used linear modulators. The use of switch type modulators provides a lower cost device with improved performance. A companion scrambling device uses similar techniques to provide improved performance at a lower cost.

Description

Description: Low cost audio scrambling and descrambling method and apparatus Background of the invention The present invention relates to low cost scrambling and descrambling techniques for audio information signals. In particular, the present invention relates to lower cost hi-fi descramblers with superior properties over the prior art. The prior art in audio scrambling and descrambling has used various frequency shifting techniques. The prior art in audio descrambling is afflicted by hiss in the form of "white noise" and, more importantly, the "whistle" of the in-band carrier caused by the intermodulation of the two carrier frequencies. The prior art also includes a bandpass filter for a mixer circuit, a wideband 0 degree and 90 degree full-band network, and a carrier frequency with adjustments that balance the gain of the quadrature mixer for low amplitude and sideband rejection. Use expensive circuits such as 0 degree and 90 degree circuits to change. In addition, mixers used in the prior art are generally not temporally stable, so their drift results in carrier leaks and audio whistles. In the prior art, a true analog multiplier is required because mixers that require ideal sinusoidal modulation are required. The circuitry of a true analog multiplier is likely to have noise problems because it produces white heat or shot noise components that degrade the signal-to-noise ratio (SNR) of the audio scrambling system. A prior art system having one or more of the same problems is described in Forbes, U.S. Pat. No. 5,058,159 issued by Kwan, published on Oct. 27, 1992, a method and system for scrambled and descrambled audio information signals, and issued on October 27, 1992, issued in Kwan No. 5,159,631. It includes an audio scrambling system that uses an in-band carrier. It would be helpful to review the prior art for a full understanding of the present invention. Turning now to the drawings, FIG. 1 is a block diagram of a prior art key element of Forbes' 853. The Forbes' 853 descrambler 10 has a scrambled audio input 34, which is connected to a full-band phase shifter 20, which includes a 0 degree output 38 and a 90 degree output. The scrambled audio signal has an offset frequency 36 (F1-F2) as shown in FIG. 2A. This indicates the offset of the scrambled audio by the offset frequency determined by the scrambling process. The phase-shifted output is connected to first inputs of linear modulators 21 and 27. The frequency generator 22 generates a square wave frequency (F1), which is fed to a bandpass filter 24 where harmonics are removed, thus resulting in a pure sine wave. This F1 sine wave is connected to the 0 degree and 90 degree phase shifters 25. The output of the phase shifter 25 is alternately connected to the second inputs of the linear modulators 21 and 27, respectively. The first and second outputs of the linear modulator are added in adder 28, and signal 37 is output. This output signal 37 is connected to the first input of the second mixer 30 via the high-pass filter 29 that passes only the F1 and the high-frequency side band as shown in FIG. 2B. The second rectangular wave frequency generator 23 generates a signal F2 as shown in FIGS. 1 and 2B. This square wave is filtered by the band-pass filter 26 to remove a harmonic, thereby outputting a pure sine wave signal. This pure sine wave signal is connected to the second input of the third mixer 30. The output of the third mixer is connected to a low-pass filter 31 and outputs a descrambled output signal 35. The second spectral diagram in FIG. 2B shows the input of the third mixer 30. Here, the frequency F1 represents a residual carrier supplied from the mixers 21 and 27. FIG. 2C shows the relationship between the frequency F1 of FIG. 2B and the carrier F2 for the scrambled audio signal shown in FIG. 2A. FIG. 2D shows the relationship between the spectral characteristics of the descrambled signal 35 and the spectral characteristics of the residual difference frequency (F1-F2) components with respect to the spectral characteristics of the signals in FIGS. 2A to 2C. FIG. 4 shows the scrambled audio input of Kwan's prior art descrambler 11. Here, a scrambled audio 40 that is offset by an offset frequency determined by the original scrambling process is shown. The scrambled audio input signal 40 is connected to an all-pass shifter 41 and outputs 0 and 90 degree phase-shifted outputs 42 and 43, and the first inputs of first and second mixers 44 and 45. To supply. The carrier frequency generator 46 generates a sine wave signal FC47 having a frequency of 1 kHz or 2-3 kHz. The carrier frequency 47 is filtered by a low pass filter 48 to remove harmonics and output a pure sine wave 49. This pure sine wave signal 49 is connected to an all-pass phase shifter 50, which outputs 0 and 90 degree signals 51 and 52, which are alternately connected to the second inputs of mixers 44 and 45. The outputs of mixers 44 and 45, signals 53 and 54, are connected to adder 55 to produce a descrambled output 56. FIG. 4B shows the relationship of the in-band descrambled carrier FC to the scrambled audio signal. In FIG. 4C, the descrambled audio spectrum is shown with a residual carrier FC that is typically −60 dB lower than the descrambled audio program, which is still audible in quiet areas of the audio program. is there. It is an object of the present invention to provide a high quality descrambler and / or a low cost frequency shifted scrambled audio signal. The described method and apparatus includes: 1) eliminating 0 degree and 90 degree phase shift circuits, 2) eliminating the use of quadrature mixer circuits, and 3) band pass or low pass filters to modulate the carrier. 4) using a switch-type mixer circuit instead of a linear mixer to reduce white noise and cost, and 5) eliminating in-band audible whistles by filtering out residual first carrier whistles. , 6) eliminates the need to tune the mixer for the smallest in-band carrier whistle; and 7) improved SNR has eliminated the need for noise reduction circuitry. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a block diagram of the key components of the Forbes prior art. FIG. 2 is a spectrum diagram of a system in the Forbes prior art. FIG. 3 is a block diagram of a prior art key component such as Kwan. FIG. 4 is a spectrum diagram of the prior art such as Kwan. FIG. 5 is a block diagram of the preferred embodiment. FIG. 6 is a spectrum diagram of a preferred embodiment of the descrambler described in FIG. FIG. 7 is a block diagram of a switch type low noise modulator. FIG. 8 is a block diagram of a first configuration example of a descrambler using the concept of the present invention. FIG. 9 is a block diagram of a second configuration example of the descrambler using the concept of the present invention. FIG. 10 is a block diagram of a third configuration example of the descrambler using the concept of the present invention. FIG. 11 is a block diagram of a preferred embodiment of a scrambler using the concept of the present invention. FIG. 12 is a spectrum diagram of the scrambler described in FIG. FIG. 13 is a configuration example of the first and second low-pass filters of the present invention. SUMMARY OF THE INVENTION The present invention is directed to a method and system for descrambling a frequency-shifted and scrambled audio signal, which satisfies the needs described above. The present invention includes a method and system for descrambling a frequency shifted and scrambled audio signal. The descramble system described above generates a modulated carrier signal at a frequency outside the original frequency spectrum range of the scrambled audio signal from about 50 Hz to about 15 kHz, thereby producing a scrambled frequency converted audio information signal. To descramble. The first modulated carrier signal generated initially has a higher frequency than the highest frequency in the original audio signal. This first modulated carrier is used to double sideband modulate the scrambled audio signal into a first modulation frequency, a first high band sideband signal, and a first low band sideband signal. . This set of signals is filtered by a filter and filtered at a first modulation frequency, all harmonics, and a high sideband signal, as well as harmonics from the two sideband signals, to form a first low sideband. The signal is passed. A second modulated carrier frequency having a lower frequency than the first modulation frequency is generated. The second modulation frequency is connected to a second modulation means for performing double sideband modulation of the first low band sideband signal together with the second modulation carrier frequency, and the second modulation frequency and the second high band side And the second lower band sideband signal. The second filter passes the second lower band sideband signal and generates a descrambled audio signal. The modulator used is a low-noise switch type modulator, which improves the signal-to-noise ratio of the descrambled signal as compared with the linear modulation conventionally used. The use of a switch-type modulator improves performance and creates a lower cost device. Pair scramblers use similar techniques and have improved performance at lower cost. A method of scrambling an original audio signal from about 50 Hz to about 15 kHz generates a first modulated carrier signal having a frequency greater than a maximum frequency in the original audio signal, and converts the original audio signal to a first lower band. Orthogonally modulates the first modulation frequency and all its harmonics from the modulated signal, and filters at least a part and all harmonics of the high-frequency sideband signal from the modulated signal. 1 to generate a second modulated carrier frequency having a frequency higher than the first modulation frequency, and to convert the first low-frequency sideband signal to the second low-frequency sideband signal. Generating a second modulation frequency, a second high-frequency sideband signal, and a second low-frequency sideband signal by performing double sideband modulation with the modulation carrier frequency of Filtering a second modulation frequency, the second high-frequency sideband signal, and the second low-frequency sideband signal to pass the second low-frequency sideband signal and scrambling Generating an audio signal. From a method perspective, the present invention provides a wide angle, scrambled audio signal by frequency transforming the original spectrum of an audio information signal to produce a modulated carrier signal having a frequency outside the frequency spectrum range of the audio information signal. Generating an information signal; and performing a first single sideband modulation by double sideband modulating the original information signal with the modulated carrier signal to convert a frequency of the original audio information signal in a predetermined direction. Contains. Preferably, the frequency of the modulated carrier signal is varied in a pseudo-random manner during generation, in particular by sweeping the frequency of the modulated carrier signal between predetermined ranges. The step of changing the frequency of the modulated carrier signal preferably includes initiating a frequency change operation in response to the first control signal at a rate determined by the second control signal. For a full understanding of the features and advantages of the present invention, the following detailed description is provided with reference to the accompanying figures. Explanation FIG. 5 is a block diagram of a preferred embodiment of the present disclosure, and FIG. 6 is a spectrum diagram thereof. FIG. 6A shows the spectral characteristics of the scrambled audio input of the preferred embodiment. Here, a scrambled audio signal offset by the offset frequency determined by the scramble processing is shown. FIG. 6B shows the relationship between the carrier of the first mixer and the output of the first mixer. The sum of both the high and low sidebands and the residual carrier FA and all these harmonics is present at the output of the first mixer. FIG. 6C shows a filter characteristic of the first LPF following the first mixer output. The first LPF filter hardly outputs the residual carrier and its higher harmonics. FIG. 6D shows the output of the spectral characteristic of the output of the first LPF following the output of the first mixer. FIG. 6E shows the relationship of the second carrier to the output of the first LPF to form the final scrambling stage. In FIG. 6F, the relationship between the descrambled audio that has passed through the second LPF with a cut-off frequency of 12 kHz and the filter outputs FB and the high-frequency sideband above FB indicates that the whistle frequency component (FA-FB) is Shown with the missing situation. The Whistle frequency component of (FA-FB) is generally -85 dB or less in descrambled audio. In the preferred embodiment, FA is about 19 kHz and FB is about 16.4 kHz. These choices are for economics so that the first LPF can be designed inexpensively at these frequencies. If higher performance is desired at a higher cost, a higher carrier frequency is used to minimize leakage from the scrambled audio input so as not to interfere with the lower sideband output of the first mixer. Can be. Note that in FIGS. 6A and 6B, there is an overlap between the spectra of the lower sideband frequencies and the scrambled audio frequencies. If the first mixer supplies enough scrambled audio, distortion will occur in the descrambled output. For example, if the carrier frequency is set to FA = 39 kHz and FB = 36.4 kHz, the scrambled input leak-through will not cause distortion to occur in the descrambled output because it is the first mixer , That is, the 2.6 to 14.6 kHz scrambled input does not overlap with the low sideband 36.4 kHz to 24 kHz. However, doubling FA and FB will increase the slope of the first LPF by about twice. This would require a higher order filter such as a 10 pole elliptical low pass filter. Minimal carrier leakage and scrambled audio leakage with lower shot noise is achieved by a double throw single pole analog switch such as 74HCT4053, or an equivalent MC1496 switch type mixer with a carrier input of, for example, 350 mV pp or more. Achieved. For example, for the CD4053 analog switch, the "on" resistance was found to be evaluated as a 400 Ω noise resistance as a result of the measured noise of 2.5 nV // Hz (/ 4 kTBr = VN = 2.5 nV // Hz). , B = 1 Hz, T = 298 ° K, k = Boltzmann constant, and R = noise resistance). The “on” resistance of CD4053 was measured at 440Ω. Thus, it has been experimentally found that the "on" resistance of an analog switch (e.g., 4053) produces the same amount of noise as a resistance component of the same resistance value. Thus, the 440 Ω “on” resistance in CD4053 has substantially the same noise as the 440 Ω resistance. A linear modulator such as the AD534 produces a noise density of 0.6 mVR MS over a 10 kHz bandwidth, or 0.6 mV // 10 kHz = 60 nV // Hz. Thus, the AD534 linear modulator is about 60/2. Generates noise five times more. This is equivalent to a 27 dB improvement when using CD4053 in linear modulation. Gilbert modulators such as 1496 or 1495 output low noise, for example> 5 nV // Hz, when the carrier input of these devices switches on and off in a differential set. This can be achieved by overlapping the carrier input with a square wave carrier input of ≧ / 200 mV or a large sine wave of> 1 V pp. If a sinusoidal modulator, such as 1495, does not have a carrier input driven to produce a linear modulation, the noise is substantially greater for a 1496 modulator in switch mode. This is because the set of two differential transistors amplifies its own noise. The internal base resistance of each transistor is typically about 50-200 ohms. If at 1495, the series internal base resistance of the two sets of differential transistors in series is 100Ω, the load at one output is 1 kΩ, and each of these transistors has a static bias of 1 mA collector current. The output noise is ＊* 1000 (gm) Vnr = V ₀ noise, gm = 38 ma / V (Ic = 1 mA). Therefore, Vnr = / 400Ω * 4kT = 2.5 nV / Hz. For a 1495 modulator, V ₀ noise = 19 * 2.5 nV // Hz = 47.5 nV // Hz. This is 19 times or 25 dB more noise than CD4053 with an "on" resistance of 440 ohms. It should be noted that in a 1495 or 1496 modulator, the output noise decreases as the carrier input increases. The key to the preferred embodiment is the use of a low pass filter (LPF) after the first mixer, which removes the residual carrier from the first mixer and removes all sidebands associated with carrier harmonics. And remove the harmonics of the carrier. If this is not done, the Whistle frequency harmonics (3FA-3FB), (5FA-5FB), etc. will appear as audible sounds in the descrambled output. This first LPF is generally a seven-pole or more elliptic filter with at least one zero tuning for selectively removing the carrier frequency FA of the first mixer. In practice, a nine-pole active filter, typically with an impedance transformer, is the best choice for a stable and accurate filter. In the preferred embodiment, the 3 dB cutoff frequency of the first low pass filter is about 17 kHz, with at least 40 dB of attenuation at 19 kHz. A detailed description of the preferred embodiment is provided below with reference to FIG. Descrambler 12 has a scrambled audio signal input 60 and includes the descrambling process of the preferred embodiment. The scrambled audio 60 is input to a first input of a first mixer 63. The second input of this first mixer is a first carrier signal FA of about 19 kHz generated by a frequency generator A61. The output of the first mixer 63 contains the carrier leakage of the FA, all sideband components and harmonics. The output of the mixer 63 is supplied to a low pass filter 65 where the first carrier, the high side band, and all harmonics are filtered from the signal 60. The output of low pass filter 65, signal 66, is provided to a first input of a second mixer 66. The second input of this second mixer is a second carrier signal FB generated by a frequency generator B62, which is 16.4 kHz, which is pseudo-randomly shifted for security reasons. 16.4 kHz ± 100 Hz. For a further description of the security process, see U.S. Pat. No. 5,095,279. The output 70 of the second mixer includes baseband descrambled audio, a residual second carrier, and sideband components above the FB frequency. The second low-pass filter 71 has a cut-off frequency of about 12 kHz and removes everything above 12 kHz, but the descrambled audio is passed to the output line 23. In the preferred embodiment described above, the mixer uses a switch-type low shot or thermal noise modulator, as illustrated in FIG. The operation of this mixer will be described with reference to the first mixer. The second mixer operates on the same principle. The scrambled audio 60 is provided to the + input of a single gain amplifier 73. The output of amplifier 73 is provided on line VIN74 to one input of a double pole single throw analog switch 32. The output of 73 is also provided to the input of a single gain inverting amplifier consisting of R2a, R2b and amplifier 65. The output of amplifier 65 is provided to a second input of switch 32 via line -VIN 75. The first carrier frequency FA is provided to a switching control input of a double pole single throw switch 32. The double pole single throw switch used is one third of the 74HCT4053, or equivalent, and is provided to the amplifier A220. A220 is a mixer output. To minimize carrier leakage at the mixer output 65, the DC zero signal voltages at the two inputs VIN and -VIN of the switching 32 must be exactly the same, eg, 0V. In addition, the inverting amplifier 73 must have a unity gain of -1 to minimize scrambled audio in the passage of (VIN). Therefore, it is required that R2a = R2b within 1% or better for the broadband operational amplifier 65 (for example, NE5532). FIG. 13A is a conventional RLC low pass filter with zeros for the descrambler's first low pass filter. The inductors L1 to L3 are considerably large at 2 mH to 20 mH for cost reduction. These low cost inductors cannot be upgraded with just the right Q at the audio frequency. A more expensive inductor with a higher Q will result in better low pass filtering, but far from the budget of a low cost descramble system. FIG. 13B shows an active 9-pole elliptic low-pass filter, which is less sensitive to component deviation than many other active filters. This is important because the frequency FA, the first carrier frequency, must be filtered below scrambled -40 dB. FIG. 13B is an active low pass filter of a typical impedance converter (GIC), which is known to provide very high performance that can be filtered at low cost. The capacitor is a 5% cheap Mylar film capacitor. The resistor is a 1% inexpensive resistor, and an operational amplifier of a general type such as TL082 or NE5532 can be used. FIG. 13C shows an example of a second filter as an active seven-pole low-pass filter. Amplifiers A1000, A2000, and A3000 can be simple voltage followers of common operational amplifiers or single transistor emitter followers. A second filter in the descrambler provides a descrambled audio signal without measurable materials such as high sidebands of a second carrier tone and / or audible artifacts, Any low pass filter, passive or active filter with sufficient stopband attenuation, can be used. 8 to 11 show various configuration examples using the concept of the present invention. In addition to the descramble system as described above, many of the same components can be used in the scrambler, and many of the same advantages achieved with the descrambler described above, for example, over prior art such as Forbes ('853). Low shot noise output and the demand for lower filters can be achieved. FIG. 11 is a block diagram of a preferred embodiment of the scrambler, and FIG. 12 is a series of spectral diagrams. An audio signal 91 with a spectral response from about 30 Hz to 15 kHz is supplied to a low pass filter 92 to remove unwanted signals above 15 kHz. Output 93 of low pass filter 92 is connected to 0 and 90 degree all-pass phase shifters 94 and 95. The outputs of the phase shifters 94 and 95 are alternately connected to first inputs of low noise modulators 96 and 97 of the switch type. The signal generator 98 generates a square wave signal of about 16.4 kHz, the 0 and 90 degrees outputs of which are connected to the second inputs of the modulators 96 and 97. The outputs of modulators 96 and 97 are summed to produce signal 103, a quadrature modulated signal that results in a residual 16.4 kHz with lower sidebands. FIG. 12 shows the relationship between the quadrature-modulated audio component and the first audio signal 91. This quadrature-modulated signal is supplied to a low-pass filter 104 to become a signal 105, which is substantially the same as the first filter of the descrambler described above. This signal 105 is connected to a first input of a third modulator 106. The modulator 106 is a switch type low heat or shot noise modulator as described above and shown in FIG. The second carrier frequency is generated by a square wave oscillator 99 that generates a frequency of about 19 kHz, as shown in FIG. 12E. The output of modulator 106 includes a 19 kHz carrier and high and low sidebands. This signal is filtered by a low pass filter 107 to produce a scrambled audio signal with an offset of about 2.6 kHz. Theoretically, in order to reduce the dynamic artifacts caused by the fast step frequency change of 16.4 kHz in both the scrambler and descrambler, the first quadrature mixer and the first mixer of both the scrambler and descrambler are used. Subsequent low pass filters should have a very matched group delay response (transfer response). If the transfer response of the low pass filter of the scrambler is different from that of the descrambler, the step change of the 16.4 kHz carrier should be slowed to minimize descramble artifacts. It has a faster step change in the safety carrier (16 kHz ± 100 Hz), has a first low-pass filter in the descrambler, and has a filter having the same characteristics as the filter 104 in the scrambler in FIG. Is preferred. Further, the second low-pass filter in the descrambler should have the same characteristics as the filter 107 of the scrambler in FIG. This allows the descrambler to quickly follow the step shift spectrum of the scrambler without the artifacts caused by the distortion of the time delay between the scrambler and the descrambler following the step shift of 16 kHz. Becomes possible. All carriers used for all mixers in the present invention of descramblers and scramblers should preferably be square wave signals to minimize artifacts. While the above is a complete description of the preferred embodiment of the present invention, various modifications, alternative constructions, and equivalents can be generated by those skilled in the art. Therefore, the above description and drawings should not be construed as limiting the scope of the invention, which is defined by the appended claims.

[Procedure amendment] Background This invention of the Patent Act 184 Article 8 [filing date] of 1995, November 7, [correction contents] specification low-cost audio scrambling and descrambling method and apparatus present invention, audio information signal Low cost scrambling and descrambling technology. In particular, the present invention relates to lower cost hi-fi descramblers with superior properties over the prior art. The prior art in audio scrambling and descrambling has used various frequency shifting techniques. The prior art in audio descrambling is afflicted by hiss in the form of "white noise" and, more importantly, the "whistle" of the in-band carrier caused by the intermodulation of the two carrier frequencies. The prior art also includes a bandpass filter for a mixer circuit, a wideband 0 degree and 90 degree full-band network, and a carrier frequency with adjustments that balance the gain of the quadrature mixer for low amplitude and sideband rejection. Use expensive circuits such as 0 degree and 90 degree circuits to change. In addition, mixers used in the prior art are generally not temporally stable, so their drift results in carrier leaks and audio whistles. In the prior art, a true analog multiplier is required because mixers that require ideal sinusoidal modulation are required. The circuitry of a true analog multiplier is likely to have noise problems because it produces white heat or shot noise components that degrade the signal-to-noise ratio (SNR) of the audio scrambling system. A prior art system having one or more of the same problems is described in Forbes, U.S. Pat. No. 5,058,159 issued by Kwan, published on Oct. 27, 1992, a method and system for scrambled and descrambled audio information signals, and issued on October 27, 1992, issued in Kwan No. 5,159,631. It includes an audio scrambling system that uses an in-band carrier. It would be helpful to review the prior art for a full understanding of the present invention. Turning now to the drawings, FIG. 1 is a block diagram of a prior art key element of Forbes' 853. The Forbes' 853 descrambler 10 has a scrambled audio input 34, which is connected to a full-band phase shifter 20, which includes a 0 degree output 38 and a 90 degree output. The scrambled audio signal has an offset frequency 36 (F1-F2) as shown in FIG. 2A. This indicates the offset of the scrambled audio by the offset frequency determined by the scrambling process. The phase-shifted output is connected to first inputs of linear modulators 21 and 27. The frequency generator 22 generates a square wave frequency (F1), which is fed to a bandpass filter 24 where harmonics are removed, thus resulting in a pure sine wave. This F1 sine wave is connected to the 0 degree and 90 degree phase shifters 25. The output of the phase shifter 25 is alternately connected to the second inputs of the linear modulators 21 and 27, respectively. The first and second outputs of the linear modulator are added in adder 28, and signal 37 is output. This output signal 37 is connected to the first input of the second mixer 30 via the high-pass filter 29 that passes only the F1 and the high-frequency side band as shown in FIG. 2B. The second rectangular wave frequency generator 23 generates a signal F2 as shown in FIGS. 1 and 2B. This square wave is filtered by the band-pass filter 26 to remove a harmonic, thereby outputting a pure sine wave signal. This pure sine wave signal is connected to the second input of the third mixer 30. The output of the third mixer is connected to a low-pass filter 31 and outputs a descrambled output signal 35. The second spectral diagram in FIG. 2B shows the input of the third mixer 30. Here, the frequency F1 represents a residual carrier supplied from the mixers 21 and 27. FIG. 2C shows the relationship between the frequency F1 of FIG. 2B and the carrier F2 for the scrambled audio signal shown in FIG. 2A. FIG. 2D shows the relationship between the spectral characteristics of the descrambled signal 35 and the spectral characteristics of the residual difference frequency (F1-F2) components with respect to the spectral characteristics of the signals in FIGS. 2A to 2C. Forbes encoders use sinusoidal type modulators for their carriers. The switch-type modulator disclosed in the present invention produces a lower white noise component and does not require a bandpass filter to filter the carrier. See Forbes at 44 and 62 in FIG. In a Forbes decoder, the mixer or multiplier does not appear to cause noise or carrier leakage. All practical mixers and multipliers have residual white random noise and carrier leakage due to parasitic capacitance and internal circuit element mismatch (eg, transistor offset voltage). Therefore, Forbes does not specifically consider residual carrier leakage from the first mixer output, intermodulation of the two carrier frequencies, and harmonics of the two carrier frequencies used to decode the scrambled audio signal. Produces an in-band whistle tone. First, consider residual carrier leakage as a problem for high quality (signal to noise ratio) decoding. This means that, first, carrier leakage from the first mixer or multiplier must be used with a particular filter. This filter after the first mixing stage must filter out carrier leakage and harmonics of carrier leakage sufficiently to obtain a whistle-free decoded output. Forbes has not tested this issue. Second, for a sine wave mixer in Forbes, there is a need to reduce random noise with a switch-type mixer. Switch-type mixers will not be able to achieve analog-type properties by a sufficient amount (eg,> 10 dB). Forbes has not tested for random white noise in multipliers or mixers. FIG. 4 shows the scrambled audio input of Kwan's prior art descrambler 11. Here, a scrambled audio 40 that is offset by an offset frequency determined by the original scrambling process is shown. The scrambled audio input signal 40 is connected to an all-pass shifter 41 and outputs 0 and 90 degree phase-shifted outputs 42 and 43, and the first inputs of first and second mixers 44 and 45. To supply. The carrier frequency generator 46 generates a sine wave signal FC47 having a frequency of 1 kHz or 2-3 kHz. The carrier frequency 47 is filtered by a low pass filter 48 to remove harmonics and output a pure sine wave 49. This pure sine wave signal 49 is connected to an all-pass phase shifter 50, which outputs 0 and 90 degree signals 51 and 52, which are alternately connected to the second inputs of mixers 44 and 45. The outputs of mixers 44 and 45, signals 53 and 54, are connected to adder 55 to produce a descrambled output 56. FIG. 4B shows the relationship of the in-band descrambled carrier FC to the scrambled audio signal. In FIG. 4C, the descrambled audio spectrum is shown with a residual carrier FC that is typically −60 dB lower than the descrambled audio program, which is still audible in quiet areas of the audio program. is there. It is an object of the present invention to provide a high quality descrambler and / or a low cost frequency shifted scrambled audio signal. The described method and apparatus includes: 1) eliminating 0 degree and 90 degree phase shift circuits, 2) eliminating the use of quadrature mixer circuits, and 3) band pass or low pass filters to modulate the carrier. 4) using a switch-type mixer circuit instead of a linear mixer to reduce white noise and cost, and 5) eliminating in-band audible whistles by filtering the residual first carrier whistle. , 6) eliminates the need to adjust the mixer for minimal in-band carrier whistle, and 7) improves SNR, thereby eliminating the need for noise reduction circuitry. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the key components of the Forbes prior art. FIG. 2 is a spectrum diagram of a system in the Forbes prior art. FIG. 3 is a block diagram of a prior art key component such as Kwan. FIG. 4 is a spectrum diagram of the prior art such as Kwan. FIG. 5 is a block diagram of the preferred embodiment. FIG. 6 is a spectrum diagram of a preferred embodiment of the descrambler described in FIG. FIG. 7 is a block diagram of a switch type low noise modulator. FIG. 8 is a block diagram of a first configuration example of a descrambler using the concept of the present invention. FIG. 9 is a block diagram of a second configuration example of the descrambler using the concept of the present invention. FIG. 10 is a block diagram of a third configuration example of the descrambler using the concept of the present invention. FIG. 11 is a block diagram of a preferred embodiment of a scrambler using the concept of the present invention. FIG. 12 is a spectrum diagram of the scrambler described in FIG. FIG. 13 is a configuration example of the first and second low-pass filters of the present invention. SUMMARY OF THE INVENTION The present invention relates to a method and system for descrambling a frequency-shifted and scrambled audio signal, which satisfies the needs described above. The present invention includes a method and system for descrambling a frequency shifted and scrambled audio signal. The descramble system described above generates a modulated carrier signal at a frequency outside the original frequency spectrum range of the scrambled audio signal from about 50 Hz to about 15 kHz, thereby producing a scrambled frequency converted audio information signal. To descramble. The first modulated carrier signal generated initially has a higher frequency than the highest frequency in the original audio signal. This first modulated carrier is used to double sideband modulate the scrambled audio signal into a first modulation frequency, a first high band sideband signal, and a first low band sideband signal. . This set of signals is filtered by a filter and filtered at a first modulation frequency, all harmonics, and a high sideband signal, as well as harmonics from the two sideband signals, to form a first low sideband. The signal is passed. A second modulated carrier frequency having a lower frequency than the first modulation frequency is generated. The second modulation frequency is connected to a second modulation means for performing double sideband modulation of the first low band sideband signal together with the second modulation carrier frequency, and the second modulation frequency and the second high band side And the second lower band sideband signal. The second filter passes the second lower band sideband signal and generates a descrambled audio signal. The modulator used is a low-noise switch type modulator, which improves the signal-to-noise ratio of the descrambled signal as compared with the linear modulation conventionally used. The use of a switch-type modulator improves performance and creates a lower cost device. Pair scramblers use similar techniques and have improved performance at lower cost. A method of scrambling an original audio signal from about 50 Hz to about 15 kHz generates a first modulated carrier signal having a frequency greater than a maximum frequency in the original audio signal, and converts the original audio signal to a first lower band. Orthogonally modulates the first modulation frequency and all its harmonics from the modulated signal, and filters at least a part and all harmonics of the high-frequency sideband signal from the modulated signal. 1 to generate a second modulated carrier frequency having a frequency higher than the first modulation frequency, and to convert the first low-frequency sideband signal to the second low-frequency sideband signal. Generating a second modulation frequency, a second high-frequency sideband signal, and a second low-frequency sideband signal by performing double sideband modulation with the modulation carrier frequency of Filtering a second modulation frequency, the second high-frequency sideband signal, and the second low-frequency sideband signal to pass the second low-frequency sideband signal and scrambling Generating an audio signal. From a method perspective, the present invention provides a wide angle, scrambled audio signal by frequency transforming the original spectrum of an audio information signal to produce a modulated carrier signal having a frequency outside the frequency spectrum range of the audio information signal. Generating an information signal; and performing a first single sideband modulation by double sideband modulating the original information signal with the modulated carrier signal to convert a frequency of the original audio information signal in a predetermined direction. Contains. Preferably, the frequency of the modulated carrier signal is varied in a pseudo-random manner during generation, in particular by sweeping the frequency of the modulated carrier signal between predetermined ranges. The step of changing the frequency of the modulated carrier signal preferably includes initiating a frequency change operation in response to the first control signal at a rate determined by the second control signal. For a full understanding of the features and advantages of the present invention, the following detailed description is provided with reference to the accompanying figures. Illustration 5 is a block diagram of a preferred embodiment of the present disclosure, FIG. 6 is its spectral diagram. FIG. 6A shows the spectral characteristics of the scrambled audio input of the preferred embodiment. Here, a scrambled audio signal offset by the offset frequency determined by the scramble processing is shown. FIG. 6B shows the relationship between the carrier of the first mixer and the output of the first mixer. The sum of both the high and low sidebands and the residual carrier FA and all these harmonics is present at the output of the first mixer. FIG. 6C shows a filter characteristic of the first LPF following the first mixer output. The first LPF filter hardly outputs the residual carrier and its higher harmonics. FIG. 6D shows the output of the spectral characteristic of the output of the first LPF following the output of the first mixer. FIG. 6E shows the relationship of the second carrier to the output of the first LPF to form the final scrambling stage. In FIG. 6F, the relationship between the descrambled audio that has passed through the second LPF with a cut-off frequency of 12 kHz and the filter outputs FB and the high-frequency sideband above FB indicates that the whistle frequency component (FA-FB) is Shown with the missing situation. The Whistle frequency component of (FA-FB) is generally -85 dB or less in descrambled audio. In the preferred embodiment, FA is about 19 kHz and FB is about 16.4 kHz. These choices are for economics so that the first LPF can be designed inexpensively at these frequencies. If higher performance is desired at a higher cost, a higher carrier frequency is used to minimize leakage from the scrambled audio input so as not to interfere with the lower sideband output of the first mixer. Can be. Note that in FIGS. 6A and 6B, there is an overlap between the spectra of the lower sideband frequencies and the scrambled audio frequencies. If the first mixer supplies enough scrambled audio, distortion will occur in the descrambled output. For example, if the carrier frequency is set to FA = 39 kHz and FB = 36.4 kHz, the scrambled input leak-through will not cause distortion to occur in the descrambled output because it is the first mixer , That is, the 2.6 to 14.6 kHz scrambled input does not overlap with the low sideband 36.4 kHz to 24 kHz. However, doubling FA and FB will increase the slope of the first LPF by about twice. This would require a higher order filter such as a 10 pole elliptical low pass filter. Minimal carrier leakage and scrambled audio leakage with lower shot noise is achieved by a double throw single pole analog switch such as 74HCT4053, or an equivalent MC1496 switch type mixer with a carrier input of, for example, 350 mV pp or more. Achieved. For example, for the CD4053 analog switch, the "on" resistance was found to evaluate to a 400 Ω noise resistance as a result of the measured noise of 2.5 nV // Hz (/ 4 kTBr = VN = 2.5 nV // Hz). , B = 1 Hz, T = 298 ° K, k = Boltzmann constant, and R = noise resistance). The “on” resistance of CD4053 was measured at 440Ω. Thus, it has been experimentally found that the "on" resistance of an analog switch (eg, 4053) produces the same amount of noise as a resistance component of the same resistance value. Thus, the 440 Ω “on” resistance in CD4053 has substantially the same noise as the 440 Ω resistance. A linear modulator such as the AD534 produces a noise density of 0.6 mVR MS over a 10 kHz bandwidth, or 0.6 mV // 10 kHz = 60 nV // Hz. Thus, the AD534 linear modulator is about 60/2. Generates noise five times more. This is equivalent to a 27 dB improvement when using CD4053 in linear modulation. Gilbert modulators such as 1496 or 1495 output low noise, for example> 5 nV // Hz, when the carrier input of these devices switches on and off in a differential set. This can be achieved by overlapping the carrier input with a square wave carrier input of ≧ / 200 mV or a large sine wave of> 1 V pp. If a sinusoidal modulator, such as 1495, does not have a carrier input driven to produce a linear modulation, the noise is substantially greater for a 1496 modulator in switch mode. This is because the set of two differential transistors amplifies its own noise. The internal base resistance of each transistor is typically about 50-200 ohms. If at 1495, the series internal base resistance of the two sets of differential transistors in series is 100Ω, the load at one output is 1 kΩ, and each of these transistors has a static bias of 1 mA collector current. In this case, the output noise is ＊* 1000 (gm) Vnr = V ₀ noise, gm = 38 ma / V (Ic = 1 mA). Therefore, Vnr = / 400Ω * 4k T = 2.5 nV / Hz. For a 1495 modulator, V ₀ noise = 19 * 2.5 nV // Hz = 47.5 nV // Hz. This is 19 times or 25 dB more noise than CD4053 with an "on" resistance of 440 ohms. It should be noted that in a 1495 or 1496 modulator, the output noise decreases as the carrier input increases. The key to the preferred embodiment is the use of a low pass filter (LPF) after the first mixer, which removes the residual carrier from the first mixer and removes all sidebands associated with carrier harmonics. And remove the harmonics of the carrier. If this is not done, the Whistle frequency harmonics (3FA-3FB), (5FA-5FB), etc. will appear as audible sounds in the descrambled output. This first LPF is generally a seven-pole or more elliptic filter with at least one zero tuning for selectively removing the carrier frequency FA of the first mixer. In practice, a nine-pole active filter, typically with an impedance transformer, is the best choice for a stable and accurate filter. In the preferred embodiment, the 3 dB cutoff frequency of the first low pass filter is about 17 kHz, with at least 40 dB of attenuation at 19 kHz. A detailed description of the preferred embodiment is provided below with reference to FIG. Descrambler 12 has a scrambled audio signal input 60 and includes the descrambling process of the preferred embodiment. The scrambled audio 60 is input to a first input of a first mixer 63. The second input of this first mixer is a first carrier signal FA of about 19 kHz generated by a frequency generator A61. The output of the first mixer 63 contains the carrier leakage of the FA, all sideband components and harmonics. The output of the mixer 63 is supplied to a low pass filter 65 where the first carrier, the high side band, and all harmonics are filtered from the signal 60. The output of low pass filter 65, signal 66, is provided to a first input of a second mixer 66. The second input of this second mixer is a second carrier signal FB generated by a frequency generator B62, this frequency FB being 16.4 kHz, which is pseudo-randomly shifted for security reasons. 16.4 kHz ± 100 Hz. See US Pat. No. 5,095,279 for a further description of security processing. The output 70 of the second mixer includes baseband descrambled audio, a residual second carrier, and sideband components above the FB frequency. The second low-pass filter 71 has a cut-off frequency of about 12 kHz and removes all frequencies above 12 kHz, but the descrambled audio is passed to the output line 23. In the preferred embodiment described above, the mixer uses a switch-type low shot or thermal noise modulator, as illustrated in FIG. The operation of this mixer will be described with reference to the first mixer. The second mixer operates on the same principle. The scrambled audio 60 is provided to the + input of a single gain amplifier 73. The output of amplifier 73 is provided on line VIN74 to one input of a double pole single throw analog switch 32. The output of 73 is also provided to the input of a single gain inverting amplifier consisting of R2a, R2b and amplifier 65. The output of amplifier 65 is provided to a second input of switch 32 via line -VIN 75. The first carrier frequency FA is provided to a switching control input of a double pole single throw switch 32. The double pole single throw switch used is one third of the 74HCT4053, or equivalent, and is provided to the amplifier A220. A220 is a mixer output. To minimize carrier leakage at the mixer output 65, the DC zero signal voltages at the two inputs VIN and -VIN of the switching 32 must be exactly the same, eg, 0V. In addition, the inverting amplifier 73 must have a unity gain of -1 to minimize scrambled audio in the passage of (VIN). Therefore, it is required that R2a = R2b within 1% or better for the wideband operational amplifier 65 (for example, NE5532). FIG. 13A is a conventional RLC low pass filter with zeros for the descrambler's first low pass filter. The inductors L1 to L3 are considerably large at 2 mH to 20 mH for cost reduction. These low cost inductors cannot be upgraded with just the right Q at the audio frequency. A more expensive inductor with a higher Q will result in better low pass filtering, but far from the budget of a low cost descramble system. FIG. 13B shows an active 9-pole elliptic low-pass filter, which is less sensitive to component deviation than many other active filters. This is important because the frequency FA, the first carrier frequency, must be filtered below scrambled -40 dB. FIG. 13B is an active low pass filter of a typical impedance converter (GIC), which is known to provide very high performance that can be filtered at low cost. The capacitor is a 5% cheap Mylar film capacitor. The resistor is a 1% inexpensive resistor, and an operational amplifier of a general type such as TL082 or NE5532 can be used. FIG. 13C shows an example of a second filter as an active seven-pole low-pass filter. Amplifiers A1000, A2000, and A3000 can be simple voltage followers of common operational amplifiers or single transistor emitter followers. A second filter in the descrambler provides a descrambled audio signal without measurable materials such as high sidebands of a second carrier tone and / or audible artifacts, Any low pass filter, passive or active filter with sufficient stopband attenuation, can be used. 8 to 11 show various configuration examples using the concept of the present invention. In addition to the descramble system as described above, many of the same components can be used in the scrambler, and many of the same advantages achieved with the descrambler described above, for example, over prior art such as Forbes ('853). Low shot noise output and the demand for lower filters can be achieved. FIG. 11 is a block diagram of a preferred embodiment of the scrambler, and FIG. 12 is a series of spectral diagrams. An audio signal 91 with a spectral response from about 30 Hz to 15 kHz is supplied to a low pass filter 92 to remove unwanted signals above 15 kHz. Output 93 of low pass filter 92 is connected to 0 and 90 degree all-pass phase shifters 94 and 95. The outputs of the phase shifters 94 and 95 are alternately connected to first inputs of low noise modulators 96 and 97 of the switch type. The signal generator 98 generates a square wave signal of about 16.4 kHz, the 0 and 90 degrees outputs of which are connected to the second inputs of the modulators 96 and 97. The outputs of modulators 96 and 97 are summed to produce signal 103, a quadrature modulated signal that results in a residual 16.4 kHz with lower sidebands. FIG. 12 shows the relationship between the quadrature-modulated audio component and the first audio signal 91. This quadrature-modulated signal is supplied to a low-pass filter 104 to become a signal 105, which is substantially the same as the first filter of the descrambler described above. This signal 105 is connected to a first input of a third modulator 106. The modulator 106 is a switch type low heat or shot noise modulator as described above and shown in FIG. The second carrier frequency is generated by a square wave oscillator 99 that generates a frequency of about 19 kHz, as shown in FIG. 12E. The output of modulator 106 includes a 19 kHz carrier and high and low sidebands. This signal is filtered by low pass filter 107 to produce a scrambled audio signal with an offset of about 2.6 kHz. Theoretically, in order to reduce the dynamic artifacts caused by the fast step frequency change of 16.4 kHz in both the scrambler and descrambler, the first quadrature mixer and the first mixer of both the scrambler and descrambler are used. Subsequent low pass filters should have a very matched group delay response (transfer response). If the transfer response of the low pass filter of the scrambler is different from that of the descrambler, the step change of the 16.4 kHz carrier should be slowed to minimize descramble artifacts. It has a faster step change in the safety carrier (16 kHz ± 100 Hz), has a first low-pass filter in the descrambler, and has a filter having the same characteristics as the filter 104 in the scrambler in FIG. Is preferred. Further, the second low-pass filter in the descrambler should have the same characteristics as the filter 107 of the scrambler in FIG. This allows the descrambler to quickly follow the step shift spectrum of the scrambler without the artifacts caused by the distortion of the time delay between the scrambler and the descrambler following the step shift of 16 kHz. Becomes possible. All carriers used for all mixers in the present invention of descramblers and scramblers should preferably be square wave signals to minimize artifacts. While the above is a complete description of the preferred embodiment of the present invention, various modifications, alternative constructions, and equivalents can be generated by those skilled in the art. Therefore, the above description and drawings should not be construed as limiting the scope of the invention, which is defined by the appended claims. Claims 1. A system for descrambling a scrambled frequency-converted audio signal capable of reproducing a spectral range of an original audio signal from about 50 Hz to about 15 kHz, the scrambled audio input having a frequency range from 50 Hz to substantially 15 kHz. Means for generating a first modulated carrier signal having a frequency greater than a maximum frequency in the original audio signal; and converting the scrambled audio signal to the first modulated frequency, a first high-frequency side. First modulation means for performing double sideband modulation on a band signal and a first low-frequency sideband signal; the first modulation frequency, all its harmonics, the high-frequency sideband signal and its harmonics Is filtered from the double sideband signal and the first low band side A first filtering means for passing a second modulation carrier frequency having a frequency lower than the first modulation frequency; a second filtering means for generating a second modulation carrier frequency having a frequency lower than the first modulation frequency; A second modulating means for performing double sideband modulation at a modulated carrier frequency to generate a second modulation frequency, a second high-frequency sideband signal, and a second low-frequency sideband signal; Filtering means for outputting a descrambled audio signal through a band sideband signal, said first and second modulated carrier signals, said first and second modulating means, and said first and second modulated signals. Generating a descrambled signal that is substantially free of audible whistle components by using and selecting the filtering means. 2. The system of claim 1, wherein said means for generating said first and second modulated carriers comprises a square wave generator. 3. The system of claim 1, wherein the first and second modulating means include a switch-type low noise modulator. 4. The system of claim 1, wherein the first filtering means comprises an elliptic filter including at least seven poles and zero for removing the first carrier frequency. 5. The system of claim 1, wherein said first filtering means comprises an active filter including at least seven poles with a conventional impedance converter. 6. The system of claim 1, wherein said second filtering means comprises a filter having seven or more poles. 7. The system of claim 1, wherein the first modulated carrier generates a frequency of at least 19kHz. 8. The system of claim 1, wherein the second modulated carrier generates a frequency at least 500 Hz below the frequency of the first modulated frequency. 9. 9. The system of claim 8, wherein the second modulated carrier is pseudo-randomly varied about +/- 100 Hz. 10. 4. The system of claim 3, wherein the first and second switch type low noise modulators include an MC1496 modulator. 11. The system of claim 3, wherein the first switch type low noise modulator includes an analog switch coupled to an opposite polarity of the scrambled audio input signal. 12. 4. The system of claim 3, wherein the second switch type low noise modulator includes an analog switch coupled to the positive and negative polarities of the first lower sideband signal. 13. A method for descrambling a scrambled frequency spectrum transformed single sideband audio information signal capable of reproducing an original audio signal having a frequency range of about 50 Hz to about 15 kHz, comprising: a scrambled frequency sideband signal; And generating a first modulated carrier signal having a frequency greater than a maximum frequency of the audio input signal, and converting the scrambled audio signal to the first modulation frequency, a first high-frequency sideband signal. And double sideband modulating the first low frequency sideband signal, the first modulation frequency, all its harmonics, the high frequency sideband signal, all its harmonics, and the low frequency sideband. All harmonics of the band from the double sideband signal Pass the low-frequency sideband signal to generate a second modulated carrier frequency having a lower frequency than the first modulation frequency; A second modulation frequency, a second high-frequency sideband signal and a second low-frequency sideband signal to generate a second modulation frequency, a second high-frequency sideband signal, and a second low-frequency sideband signal. Generating the descrambled audio signal by filtering the high-side band signal and passing the second low-side band signal, the first and second modulation signals; Generating said descrambled audio signal substantially free of audible whistle components through the use and selection of and second modulation means and said first and second filtering means. Wherein the. 14． 14. The method of claim 13, wherein said means for generating said first and second modulated carriers comprises a square wave generator. 15. 14. The method of claim 13, wherein the double sideband modulator comprises a switch-type low noise modulator. 16. Filtering the first modulation frequency and all its harmonics, the high sideband signal and all its harmonics from the double sideband signal and passing the low sideband signal comprises at least 7 14. The method of claim 13, wherein an elliptic filter is used that includes a pole and zero to remove the first carrier frequency. 17． Filtering the first modulation frequency and all its harmonics, the high sideband signal and all its harmonics from the double sideband signal and passing the low sideband signal is a normal step. 14. The method according to claim 13, wherein an active filter including at least seven poles is used with an impedance converter. 18. 14. The method of claim 13, wherein the second filtering of a second modulation frequency, a second high sideband signal, and a second low sideband signal comprises a filter with seven or more poles. 19. 14. The method of claim 13, wherein the first modulated carrier generates a frequency of at least 19kHz. 20. 14. The method of claim 13, wherein the second modulated carrier generates a frequency that is at least 500 Hz lower than the first modulated carrier. 21. 14. The method of claim 13, wherein the second modulated carrier generates a frequency that is about 2.6 kHz lower than the first modulated carrier. 22. 14. The method of claim 13, wherein the second modulated carrier generates a pseudo-randomly varied frequency. 23. The method of claim 15, wherein the first and second switch type low noise modulators include a switched Gilbert multiplier. 24. 16. The method of claim 15, wherein the first switch type low noise modulator includes an analog switch coupled to a positive polarity and a negative polarity and a part polarity of the scrambled audio input signal. 25. 16. The method of claim 15, wherein the second switch type low shot noise modulator includes an analog switch coupled to the positive and negative polarities of the first low sideband signal. 26. The method of claim 15, wherein the first switch type low noise modulator comprises a chopper switch modulator. 27. 17. The method of claim 16, wherein the second switch type low shot noise modulator comprises a chopper switch modulator. 28. A scrambling system for an original audio signal from about 50 Hz to about 15 kHz, comprising: an audio input signal in a frequency range from 50 Hz to 15 kHz; and a first modulated carrier having a frequency greater than a maximum frequency in the original audio signal. Means for generating a signal; first modulating means for quadrature sideband modulating the original audio signal into a first lower band sideband signal; said first modulation frequency and at least many of its harmonics; First filtering means for filtering a high-frequency sideband signal and its harmonics from the quadrature signal and passing the first low-frequency sideband signal; and a second filter having a frequency higher than the first modulation frequency. Means for generating a second modulated carrier frequency; and converting the first lower sideband signal to the second modulated carrier frequency. A second modulation unit that performs double sideband modulation with a wave number to output a second modulation frequency, a second high-frequency sideband signal, and a second low-frequency sideband signal; Filtering means for outputting a scrambled audio signal through a sideband signal, said first and second modulated carrier signals, said first and second modulating means, and said first and second filtering means Generating a scrambled audio signal with lower noise levels and fewer components through the use and selection of an audio signal. 29. 29. The system of claim 28, wherein said means for generating said first and second modulated carriers comprises a square wave generator. 30. 29. The system of claim 28, wherein said second modulation means comprises a switch-type low noise modulator. 31. 29. The system of claim 28, wherein said first filtering means comprises an elliptic filter including at least seven poles. 32. 29. The system of claim 28, wherein said first filtering means includes a filter that does not need to be tuned to said first frequency. 33. 29. The system of claim 28, wherein said first filtering means comprises an active filter including at least seven poles with a conventional impedance converter. 34. 29. The system of claim 28, wherein said second filtering means comprises a filter having seven or more poles. 35. 29. The system of claim 28, wherein the first modulated carrier generates a frequency of at least 16.4kHz. 36. 29. The system of claim 28, wherein the second modulated carrier generates a frequency that is at least 500 Hz higher than the first modulated carrier. 37. 29. The system of claim 28, wherein the second modulated carrier generates a frequency that is pseudorandomly varied by about +/- 100 Hz. 38. 29. The system of claim 28, wherein the switch type low noise modulator comprises a differential pair balanced multiplication type modulator. 39. 29. The system of claim 28, wherein the second switch type low noise modulator includes an analog switch coupled to an opposite polarity of the first higher sideband signal. 40. A method for scrambling an original audio signal from about 50 Hz to about 15 kHz, comprising: inputting an audio signal within a frequency range from 50 Hz to 15 kHz; and a first modulation having a frequency greater than a maximum frequency in the original audio signal. Generating a carrier signal, quadrature modulating said original audio signal into a first lower sideband signal, said first modulation frequency and all its harmonics, said higher sideband signal and all its Filtering the harmonics from the modulated signal and passing the first lower sideband signal to generate a second modulated carrier frequency having a higher frequency than the first modulation frequency; At the second modulation carrier frequency and the second modulation frequency and the second high frequency sideband. And outputting the second modulation frequency, the second high-frequency sideband signal, and the second low-frequency sideband signal. Outputting the audio signal scrambled through the second lower band sideband signal, the first and second modulated signals, the first and second modulating means, and the first and second modulated signals. Generating a descrambled audio signal with a lower noise level and fewer components by using and selecting the second filtering means. 41. The method of claim 40, wherein the first and second modulated carrier generators comprise square wave generators. 42. The method of claim 40, wherein the double sideband modulator comprises a switch-type low noise modulator. 43. Filtering the first modulation frequency and all its harmonics, the high sideband signal and all its harmonics from the double sideband signal and passing the low sideband signal comprises at least 7 41. The method of claim 40, wherein an elliptic filter including a tuned zero tuning notch is used to remove poles and the first carrier frequency. 44. Filtering the first modulation frequency and all its harmonics, the high sideband signal and all its harmonics from the double sideband signal and passing the low sideband signal is a normal step. 41. The method of claim 40, wherein an active filter including at least seven poles is used with an impedance converter. 45. 41. The method of claim 40, wherein the second filtering of a second modulation frequency, a second high sideband signal, and a second low sideband signal comprises a filter with seven or more poles. 46. The method of claim 40, wherein the first modulated carrier generates a frequency of at least 16.4 kHz. 47. 41. The method of claim 40, wherein the second modulated carrier generates a frequency that is at least 50 Hz higher than the first modulated carrier frequency. 48. 41. The method of claim 40, wherein the second modulated carrier generates a pseudo-randomly varied frequency for a frequency substantially equal to 19 kHz. 49. 42. The method of claim 40, wherein the switch type low noise modulator comprises a differential pair balanced multiplying type modulator. 50. 41. The method of claim 40, wherein the switch-type low noise modulator includes an analog switch coupled to the positive and negative polarities of the high sideband signal. FIG. FIG. 2 FIG. 4 FIG. 3 FIG. 5 FIG. 6 FIG. 7 FIG. 8 FIG. 9 FIG. 10 FIG. 11 FIG. FIG. 13 [Procedure amendment] [Date of submission] May 21, 1997 [Contents of amendment] Claims: "1. A modulated carrier signal at a frequency outside the original frequency spectrum range of the original audio signal from about 50 Hz to about 15 kHz. A system for descrambling a scrambled frequency converted audio information signal by generating a means for generating a first modulated carrier signal having a frequency greater than a maximum frequency in the original audio signal; First modulating means for double-sideband modulating the scrambled audio signal into the first modulation frequency, the first high-frequency sideband signal, and the first low-frequency sideband signal; The modulation frequency, all its harmonics, the high sideband signal and its harmonics into the double sidebar. First filtering means for filtering the first low-side band signal from the input signal and generating a second modulated carrier frequency having a frequency lower than the first modulation frequency; (1) double sideband modulating the first lowband sideband signal with the second modulation carrier frequency to generate a second modulation frequency, a second highband sideband signal, and a second lowband sideband signal; 2. A system comprising: a second modulating means for performing a filtering operation, and a filtering means for outputting a descrambled audio signal through the second low-frequency sideband signal 2. An original audio signal of about 50 Hz to about 15 kHz Frequency-spectrum transformed synth scrambled by generating a modulated carrier signal at a frequency outside the frequency spectrum range of A method for descrambling a glue sideband audio information signal, comprising: generating a first modulated carrier signal having a frequency greater than a maximum frequency in the original audio signal; and converting the scrambled audio signal to the first Modulating frequency, performing double sideband modulation on the first high-frequency sideband signal and the first low-frequency sideband signal, the first modulation frequency, all its harmonics, the high-frequency sideband signal, All its harmonics, and all harmonics of the lower sideband, are filtered from the double sideband signal and passed through the lower sideband signal, having a lower frequency than the first modulation frequency A second modulated carrier frequency is generated, and the first lower sideband signal is double-sized at the second modulated carrier frequency. Generating a second modulation frequency, a second high-frequency sideband signal, and a second low-frequency sideband signal, and converting the second modulation frequency and the second high-frequency sideband signal. Filtering the second low band sideband signal to produce a descrambled audio signal. 3 . A scrambling system for an original audio signal from about 50 Hz to about 15 kHz, comprising: means for generating a first modulated carrier signal having a frequency greater than a maximum frequency in the original audio signal; First modulating means for performing quadrature sideband modulation on a first low band sideband signal; First filtering means for filtering the signal to pass the first lower sideband signal; means for generating a second modulated carrier frequency having a frequency higher than the first modulation frequency; 1 is double-sideband-modulated with the second modulation carrier frequency to obtain a second modulation frequency and a second high-frequency signal. A system comprising: a second modulator for outputting a side band signal and a second lower band sideband signal; and a filtering unit for outputting an audio signal scrambled through the second lower band sideband signal. . 4 . A method for scrambling an original audio signal from about 50 Hz to about 15 kHz, comprising: generating a first modulated carrier signal having a frequency greater than a maximum frequency in the original audio signal; Orthogonally modulates the first modulation frequency and all its harmonics, the high frequency sideband signal and all its harmonics from the modulated signal. Generating a second modulated carrier frequency having a frequency higher than the first modulation frequency, passing the first low-frequency sideband signal through the second modulated carrier; Outputting a second modulation frequency, a second high-frequency sideband signal, and a second low-frequency sideband signal by performing double sideband modulation at the frequency; Each step of filtering a harmonic frequency, the second high-frequency sideband signal, and the second low-frequency sideband signal to output a scrambled audio signal through the second low-frequency sideband signal A method consisting of: "

────────────────────────────────────────────────── ─── Continuation of front page    (81) Designated countries EP (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, M C, NL, PT, SE), OA (BF, BJ, CF, CG , CI, CM, GA, GN, ML, MR, NE, SN, TD, TG), AP (KE, MW, SD, SZ), AM, AT, AU, BB, BG, BR, BY, CA, CH, C N, CZ, DE, DK, EE, ES, FI, GB, GE , HU, JP, KE, KG, KP, KR, KZ, LK, LR, LT, LU, LV, MD, MG, MN, MW, N L, NO, NZ, PL, PT, RO, RU, SD, SE , SI, SK, TJ, TT, UA, UZ, VN

Claims (1)

[Claims] 1. Original frequency spectrum of original audio signal from about 50Hz to about 15kHz Scrambling by generating a modulated carrier signal at frequencies outside the System that descrambles the converted frequency-converted audio information signal. So,   A first having a frequency greater than a maximum frequency in the original audio signal; Means for generating a modulated carrier signal of   Converting the scrambled audio signal to the first modulation frequency, a first high frequency Double sideband for the sideband signal and the first lowband sideband signal First modulating means for modulating;   The first modulation frequency, all its harmonics, the high sideband signal and The harmonic is filtered from the double sideband signal and the first low-frequency sideband is filtered. First filtering means for passing a command signal;   Generating a second modulated carrier frequency having a lower frequency than the first modulation frequency; Means to produce,   The first lower sideband signal is doubled at the second modulated carrier frequency. Sideband modulation, a second modulation frequency, a second high-frequency sideband signal, and a second Second modulating means for generating a low-frequency sideband signal of   Audio signal descrambled through the second lower band sideband signal Filtering means to output the signal System consisting of. 2. The means for generating the first and second modulated carriers includes a square wave generator. The system according to claim 1. 3. The first modulation means and the second modulation means are switch type low noise modulation. The system of claim 1, comprising a vessel. 4. The first filtering means comprises at least seven poles and the first carrier Includes an elliptic filter with zero to remove frequencies The system according to claim 1. 5. The first filtering means includes a normal impedance converter and a small amount. 2. The system of claim 1, including an active filter including at least seven poles. 6. The second filtering means includes a filter having seven or more poles. The system of claim 1. 7. The first modulated carrier generates a frequency of at least 19 kHz. Item 10. The system according to Item 1. 8. The second modulation carrier is at least higher than the frequency of the first modulation frequency. The system of claim 1, wherein the system generates a frequency that is 500 Hz lower. 9. The second modulated carrier is pseudo-randomly varied about +/- 100 Hz. 9. The system according to claim 8, wherein 10. The first and second switch type low noise modulators are MC1496 modulators. The system of claim 3, including a conditioner. 11. The first switch-type low noise modulator comprises the scrambled Includes analog switch coupled to opposite polarity of audio input signal The system according to claim 3. 12. The low noise modulator of the second switch type includes a first low side modulator. 7. An analog switch coupled to the positive and negative polarities of the band signal. 3. The system according to 3. 13. Original frequency spectrum of original audio signal from about 50Hz to about 15kHz By generating a modulated carrier signal at frequencies outside the Frequency spectrum converted single sideband audio information signal Is to descramble the issue   A first having a frequency greater than a maximum frequency in the original audio signal; Generating a modulated carrier signal of   Converting the scrambled audio signal to the first modulation frequency; Double the first high-frequency sideband signal and the first low-frequency sideband signal Do band modulation   The first modulation frequency, all its harmonics, the high sideband signal, All the higher harmonics and all higher harmonics of the lower band side band. Through the low band side band signal by filtering from the low band signal,   Generating a second modulated carrier frequency having a lower frequency than the first modulation frequency; Raw,   The first lower sideband signal is doubled at the second modulated carrier frequency. Sideband modulation, a second modulation frequency, a second high-frequency sideband signal, and a second To generate the lower sideband signal of   Filtering the second modulation frequency and the second high-frequency sideband signal; 2 to generate a descrambled audio signal that passes through the low-frequency sideband signal. Each stage to be completed A method consisting of: 14． The means for generating the first and second modulated carriers comprises a square wave generator. 14. The method of claim 13, comprising: 15. The double sideband modulator includes a switch type low noise modulator. The method of claim 13. 16. The first modulation frequency and all its harmonics, the high sideband Filter the signal and all its harmonics from the double sideband signal and Passing the sideband signal comprises at least seven poles and the first carrier frequency. 14. The method of claim 13, wherein an elliptic filter including zero is used to remove. 17． The first modulation frequency and all its harmonics, the high sideband Filter the signal and all its harmonics from the double sideband signal and The step of passing the sideband signal involves at least a normal impedance converter. 14. The method according to claim 13, wherein an active filter comprising seven poles is used. 18. A second modulation frequency, a second high band sideband signal and a second low band side band signal. Wherein the second filtering of the id band signal comprises a filter with more than seven poles. 14. The method of claim 13. 19. The first modulated carrier has a frequency of at least 19 kHz. 14. The method of claim 13. 20. The second modulated carrier is at least 500 times greater than the first modulated carrier. 14. The method of claim 13, wherein the method generates a frequency lower by Hz. 21. The second modulated carrier is about 26 kHz lower than the first modulated carrier 14. The method according to claim 13, wherein the frequency is generated. 22. The second modulated carrier has a frequency that can be pseudo-randomly changed. 14. The method of claim 13, wherein said method occurs. 23. The first and second switch-type low-noise modulators are switch-type Gills. The method of claim 15, including a Bart multiplier. 24. The first switch-type low noise modulator comprises the scrambled Analog coupled to positive and negative polarity and part polarity of audio input signal The method of claim 15 including a switch. 25. The second switch type low shot noise modulator includes a first low band noise modulator. Analog switches coupled to the positive and negative polarities of the sideband signal on the side The method of claim 15 comprising: 26. The low noise modulator of the first switch type comprises a chopper switch modulation The method of claim 15 including a vessel. 27. The second switch type low shot noise modulator comprises a chopper switch. 17. The method of claim 16, comprising a switch modulator. 28. Original audio signal scramble system from about 50Hz to about 15kHz System   A second one having a frequency greater than a maximum frequency in the original audio signal. Means for generating one modulated carrier signal;   Transforms the original audio signal into a quadrature sideband First modulating means for modulating;   The first modulation frequency and at least many of its harmonics, And the harmonics thereof are filtered from the quadrature signal to form the first low-side sidebar. First filtering means for passing a command signal;   Generating a second modulated carrier frequency having a higher frequency than said first modulation frequency; Means to produce,   The first lower sideband signal is double-supported at the second modulated carrier frequency. The second modulation frequency, the second high-frequency sideband signal, and the A second modulating means for outputting a low-frequency sideband signal of No. 2;   An audio signal scrambled through the second lower band sideband signal; Filtering means to output the signal System consisting of. 29. The means for generating the first and second modulated carriers comprises a square wave generator. 29. The system of claim 28, comprising: 30. 3. The second modulation means includes a switch type low noise modulator. 8. The system according to 8. 31. The first filtering means is an elliptic filter including at least seven poles 29. The system of claim 28, comprising: 32. The first filtering means needs to tune to the first frequency. 29. The system of claim 28, comprising no filter. 33. The first filtering means involves a normal impedance converter 29. The system of claim 28, including an active filter including at least seven poles. 34. The second filtering means includes a filter having seven or more poles 29. The system of claim 28. 35. The first modulated carrier generates a frequency of at least 16.4 kHz. 29. The system according to claim 28. 36. The second modulated carrier has less than the first modulated carrier. 29. The system of claim 28, wherein the system generates a frequency at least 500 Hz higher. 37. The second modulated carrier is pseudo-randomly varied about +/- 100 Hz. 29. The system of claim 28, wherein said system generates a frequency to be generated. 38. The switch type low noise modulator is a differential pair balanced multiplication type modulator. 29. The system of claim 28, comprising: 39. The second switch-type low-noise modulator includes a first switch-side low-noise modulator. 3. An analog switch coupled to the opposite polarity of the band signal. 8. The system according to 8. 40. Method for scrambling original audio signal of about 50 Hz to about 15 kHz And   A second one having a frequency greater than a maximum frequency in the original audio signal. Generating one modulated carrier signal;   Quadrature modulating the original audio signal into a first lower band sideband signal;   The first modulation frequency and all its harmonics, the high sideband signal and And filtering all of its harmonics from the modulated signal to the first lower side. Through the band signal,   Generating a second modulated carrier frequency having a higher frequency than said first modulation frequency; Raw,   The first lower sideband signal is double-supported at the second modulated carrier frequency. The second modulation frequency, the second high-frequency sideband signal, and the 2 to output the lower band sideband signal,   The second modulation frequency, the second high-frequency sideband signal, and the second Filtering the lower band sideband signal and passing through the second lower band sideband signal Each stage of outputting a scrambled audio signal A method consisting of: 41. 5. The method of claim 4, wherein the first and second modulated carrier generators include a square wave generator. 0. The method of claim 0. 42. The double sideband modulator includes a switch type low noise modulator. 41. The method of claim 40. 43. The first modulation frequency and all its harmonics, the high sideband Filter the signal and all its harmonics from the double sideband signal and Passing the sideband signal comprises at least seven poles and the first carrier frequency. Using an elliptic filter with a tuned zero tuning notch to remove noise Item 40. The method according to Item 40. 44. The first modulation frequency and all its harmonics, the high sideband Filter the signal and all its harmonics from the double sideband signal and The step of passing the sideband signal involves at least a normal impedance converter. 41. The method of claim 40, further comprising using an active filter including seven poles. 45. A second modulation frequency, a second high band sideband signal, and a second low band side The second filtering of the sideband signal includes a seven or more pole filter 41. The method of claim 40. 46. The first modulated carrier generates a frequency of at least 16.4 kHz. 41. The method of claim 40. 47. The second modulated carrier is at least higher than the first modulated carrier frequency. 41. The method of claim 40, wherein the method generates a 50 Hz higher frequency. 48. The second modulated carrier has a frequency substantially equal to 19 kHz. 41. The method of claim 40, wherein generating a pseudo-randomly varied frequency. 49. The switch type low noise modulator is a differential pair balanced multiplication type modulator. 41. The method of claim 40, comprising: 50. The switch-type low-noise modulator includes a high-frequency sideband signal. 42. The method of claim 40, comprising an analog switch coupled to a positive polarity and a negative polarity. Law.