Subscriber-limited reception television broadcast security encoder-decoder system

• US RE31,735 E
• Filed: 07/26/1982
• Issued: 11/13/1984
• Est. Priority Date: 10/19/1977
• Status: Expired due to Term

• Current Assignee: Feature Film Services
• Original Assignee: Feature Film Services
• Inventors: Davidson, Richard A.
• Primary Examiner(s): BUCZINSKI, STEPHEN C
• Application Number:
  US06/401,693
• Time in Patent Office: 841 Days
• Field of Search: 358/114, 358/117, 358/116, 358/122-124, 358/121, 179/1.5 S, 179/1.5 E
• US Class Current: 380/235
• CPC Class Codes: H04N 7/162 Authorising the user terminal, e.g. by paying; Registering the use of a subscription channel, e.g. billing
• CPC Class Codes: H04N 7/165 Centralised control of user terminal subsequent to an upstream request signal H04N7/17345; Registering at central by two-way working H04N7/17309

Abstract

A method and apparatus for encoding and decoding of standard television signals are provided for enabling reception thereof in an intelligible manner only by authorized subscribers. The scrambling of the video signals is effected by inversion of the video signals of some horizontal scan lines on a pseudo-random basis to produce a picture having some video signals inverted and others not inverted which is unpleasant to view and virtually unintelligible. The scrambling of the audio signals is effected by conversion of analog audio signals to coded digital audio signals. A plurality of unique pulse coded control signals consisting of 32-bit binary pulse trains are transmitted separately to identify individual authorized subscribers and to provide information needed to unscramble the scrambled video and audio signals. When there is a comparison between one of the pulse-coded control signals and a unique address code stored at a particular subscriber'"'"'s receiver, unscrambling of the video and audio signals occurs in the same sequence as used for scrambling so as to provide restored video and audio signals without degradation in picture and sound qualities.

Claims

1. A subscription television system for scrambling and unscrambling of standard television signals having horizontal scan lines that include horizontal synchronizing signals, vertical synchronizing signals, and video signals, and accompanying audio signals to enable reception of the video and audio signals in an intelligible manner only by authorized subscribers, said system comprising:

(1) transmitting means comprising;

(a) means for scrambling video signals by inversion of the video portion of some horizontal scan lines in a line-by-line fashion on a pseudo-random basis to produce a picture having some video signals inverted and others not inverted which produces a substantially unintelligible visual display;

(b) means for scrambling audio signals;

(c) means for generating a plurality of discrete pulse coded control signals serving to identify individual subscribers which are authorized to unscramble the scrambled video and audio signals and to provide decoding pulses;

(d) means for transmitting the scrambled video and audio signals together with the control signals, said control signals being transmitted separately and simultaneously during transmission of each of the horizontal scan lines on a separate preselected frequency distinct from the video signals to determine whether or not the video portions of the next successive horizontal scan lines is are to be inverted; and

(2) receiving means comprising;

(a) means for receiving the transmitted scrambled video and audio signals together with the control signals;

(b) means for storing a unique subscriber identity code;

(c) means for comparing each of the discrete pulse coded control signals with the stored identity code

(d) unscrambling means converting said control signals into decoding pulse and responsive to said comparing means when there is a code match for unscrambling of the video and audio signals by means of said decoding pulse in the same sequence as used for scrambling to provide restored video and audio signals without degradation in picture and sound qualities; and

(3) controlling means responsive to said plurality of control signals for continuously enabling each of the individual unscrambling means at a particular subscriber'"'"'s receiving means on a selective basis so that if the comparing means fails to produce a code match for an individual subscriber identity code before a pre-selected time interval has elapsed the unscrambling means is automatically disabled.

2. A subscription television system as claimed in claim 1, wherein said control signals are 32-bit binary pulse trains which are utilized to identify the individual subscribers and to provide different code combinations sufficient to designate up to 2³⁰ (1,073,824) different individual subscribers.

3. A subscription television system as claimed in claim 2, wherein said video scrambling means includes coding means for converting the 32-bit binary pulse trains into a plurality of 4-bit binary scrambler pattern codes.

4. A subscription television system as claimed in claim 3, wherein said coding means includes a plurality of full adder circuits having input bit location which are interchangeable on a pre-selected pattern to render high security to the 4-bit codes.

5. A subscription television system as claimed in claim 4, further comprising amplifier means responsive to one bit in each of the 4-bit codes to increase further the security for generating either an inverted or non-inverted video signal.

6. A subscription television system as claimed in claim 5, wherein said audio scrambling means includes an analog-to-digital converter to convert the analog audio signals to digitized audio signals consisting of 11-bit binary pulse trains to provide added security.

7. A subscription television system as claimed in claim 6, further comprising an additional full adder circuit which combines each of the 11-bit pulse trains with each of the 4-bit codes to generate the coded digital audio signals thereby giving increased security from unauthorized use.

8. A subscription television system as claimed in claim 7, wherein said storing means includes a read-only-memory circuit to store the unique address code consisting of a 32-bit code.

9. A subscription television system as claimed in claim 8, wherein said comparing means includes a comparator circuit to determine if any of the control signals is identical to the 32-bit code stored in the read-only-memory.

10. A subscription television system as claimed in claim 9, wherein said unscrambling means include decoding means for converting the control signals of 32-bit pulse trains into a plurality of 4-bit codes identical to the 4-bit binary scrambled pattern codes used to scramble the video and audio signals so a to decode the transmitted video and audio signals.

11. A subscription television system as claimed in claim 1, further comprising controlling means for continuously enabling the unscrambling means at a particular subscriber'"'"'s receiving means on the selective basis whereby if there is no comparison by the comparing means before a preselected time interval has elapsed the unscrambling means is disabled.

12. A subscription television system as claimed in claim 1, further comprising telephone communication means interconnected between the transmitting means and the receiving means for requesting to the transmitting means programs desired to be received at the receiving means.

13. A subscription television system as claimed in claim 1, further comprising means for transmitting aural barker signals simultaneously with the scrambled video signals and means for receiving the barker signals regardless of whether the subscriber is authorized to receive the unscrambled video signals so as to promote usage of the subscription television system.

14. A subscription television system as claimed in claim 10, further comprising controlling means for continuously enabling the decoding means at a particular subscriber'"'"'s receiving means on a selective basis whereby if there is no comparison between the control signals and the address code stored in the read-only-memory before a preselected time interval has elapsed the decoding means is disabled.

47. A subscription television system as claimed in claim 2, wherein the first bits of the 32-bit binary pulse trains are always in the low state and the last bits thereof are always in the high state so as to facilitate in detection and synchronization by said receiving means.

49. A subscription television system as claimed in claim 6, wherein the first bits of the 11-bit binary pulse trains are always in the low state and the last bits thereof are always in the high state so as to facilitate in detection and synchronization by said receiving means.

50. A subscription television system as claimed in claim 2, wherein said means for receiving the transmitted scrambled video and audio signals together with the control signals include counter circuitry to sample and detect the contents of the 32-bit binary pulse trains and a shift register to convert the serial inputs of the pulse trains to a parallel output.

51. A subscription television system as claimed in claim 49, wherein said means for receiving the transmitted scrambled video and audio signals together with the control signals further include an additional counter to sample and the content of the 11-bit binary pulse trains and a shift register to convert the series inputs of the pulse trains to a parallel output.

52. A subscription television system as claimed in claim 12, wherein said telephone communication means includes a plurality of buttons to allow a subscriber to place a request to the transmitting means.

53. A subscription television system as claimed in claim 52, wherein said telephone communication means further includes a dial tone detector to determine when telephone lines are clear for transmission of a dial address to the transmitting means.

54. A subscription television system as claimed in claim 53, wherein said telephone communication means further includes a carrier tone detector to determine when the transmitting means is ready to receive the subscriber'"'"'s account code and request codes.

55. A subscription television system as claimed in claim 53, wherein said telephone communication means further includes a multi-frequency tone generator for dialing the transmitter means.

56. A subscription television system as claimed in claim 53, wherein said telephone communication means further includes a programmable divide-by-N counter to to cause various number of contact closure interruptions to dial the transmitting means.

57. A subscription television system as claimed in claim 55, further including a voltage-to-frequency converter for transmitting the subscriber'"'"'s account code and request codes.

58. A subscription television system as claimed in claim 54, further including an acknowledgment tone detector to determine the successful completion of transmitting the subscriber'"'"'s account code and request codes.

59. A subscription television system as claimed in claim 58, further including indicating means to visually display a successful completion of request or a failure of a completion.

60. A subscription television system as claimed in claim 52, wherein said telephone communication means includes a timer circuit to reset the subscriber'"'"'s if it is not completed within a pre-determined time interval.

61. A subscription television system as claimed in claim 1, wherein said means for unscrambling of the video and audio signals includes modulator means to convert the restored video and audio signals to a desired locally unused VHF channel as the secure channel.

62. A subscription television system as claimed in claim 1, further comprises RF splitter and combiner circuits to permit viewing of all of the other unscrambled television channels unaffected by the scrambling means.

63. A subscription television system as claimed in claim 1, further comprising a phase-locked master clock for synchronizing the control signals to a horizontal scanning rate utilized by the transmitting means.

64. The subscription television system of claim 1 wherein the means for scrambling audio signals includes means for conversion of analog audio signals to coded digital audio signals. .Iadd.

15. For use in a subscription television system, a method for scrambling and unscrambling of standard television signals having horizontal scan lines that include horizontal synchronizing signals, vertical synchronizing signals, and video signals, and accompanying audio signals to enable reception of the video and audio signals in an intelligible manner only by authorized subscribers, said method comprising the steps of:

scrambling video signals by inversion of the video signals of some horizontal scan lines on a line-by line fashion in a pseudo-random basis to produce a picture having some video signals inverted and others not inverted which is unpleasant to view and virtually unintelligible;

scrambling audio signals by conversion of analog audio signals to coded digital audio signals;

generating a plurality of unique pulse coded control signals serving to identify individual subscribers which are authorized to unscramble the scrambled video and audio signals;

transmitting the scrambled video and audio signals together with the control signals, said control signals being transmitted separately and simultaneously during each of the horizontal scan lines to determine whether or not the video portion of the next successive horizontal scan line is to be inverted;

receiving the transmitted scrambled video and audio signals together with the control signals;

storing a unique address code to identify a particular subscriber;

comparing each of the pulse coded control signals with the stored address code;

unscrambling of the video and audio signals by means of decoding pulses converted from said control signals in the same sequence as used for scrambling when the step of comparing indicates a match to provide restored video and audio signals without degradation in picture and sound qualities; and

enabling continuously the unscrambling step at each individual subscriber'"'"'s unit on a selective basis so that if there is no match by the comparing step before a pre-selected time interval has elapsed the step of unscrambling is automatically disabled.

16. A method for scrambling and unscrambling of standard television signals as claimed in claim 15, wherein said control signals are 32-bit binary pulse trains which are utilized to identify the individual subscribers and to provide different code combinations sufficient to designate up to 2³⁰ (1,073,741,824) different individual subscribers.

17. A method for scrambling and unscrambling of standard television signals as claimed in claim 16, wherein said video scrambling step includes the step of coding by converting the 32-bit binary pulse trains into a plurality of 4-bit binary scrambler pattern codes.

18. A method for scrambling and unscrambling of standard television signals as claimed in claim 17, wherein said coding step includes the step of interchanging the input bit locations of a plurality of full adder circuits on a pre-selected pattern to render high security to the 4-bit codes.

25. A method for scrambling and unscrambling of standard television signals as claimed in claim 15, further comprising the steps of controlling and enabling continuously the unscrambling step on a selective basis so that if there is no match by the comparing step before a pre-selected time interval has elapsed the step of unscrambling is disabled.

26. A method for scrambling and unscrambling of standard television signals as claimed in claim 15, further comprising the step of requesting by telephone communication programs desired to be received.

27. A method for scrambling and unscrambling of standard television signals as claimed in claim 15, further comprising the steps of transmitting aural barker signals simultaneously with the scrambled video signals and receiving the barker signals regardless of whether the subscriber is authorized to receive the unscrambled video signals so as to promote usage of the subscription television system.

19. A method for scrambling and unscrambling of standard television signals as claimed in claim 19, further comprising the step of providing an amplifier responsive to one bit in each of the 4-bit codes to increase further the security for generating either an inverted or non-inverted video signal.

20. A method for scrambling and unscrambling of standard television signals as claimed in claim 19, wherein said audio scrambling step includes the step of providing an analog-to-digital converter to convert the analog audio signals to digitized audio signals consisting of 11-bit binary pulse trains to provide added security.

21. A method for scrambling and unscrambling of standard television signals as claimed in claim 20, further comprising the step of combining each of the 11-bit pulse trains with each of the 4-bit codes to generate the coded digital audio signals thereby giving increased security from unauthorized use.

22. A method for scrambling and unscrambling of standard television signals as claimed in claim 21, wherein said storing step includes the step of providing a read-only-memory circuit to store the unique address code consisting of a 32-bit code.

23. A method for scrambling and unscrambling of standard television signals as claimed in claim 22, wherein said comparing step includes the step of providing a comparator circuit to determine if any of the control signals is identical to the 32-bit code stored in the read-only-memory.

24. A method for scrambling and unscrambling of standard television signals as claimed in claim 23, wherein said unscrambling step further comprises the step of decoding by converting the control signals of 32-bit pulse trains into a plurality of 4-bit codes identical to the 4-bit binary scrambled pattern codes used to scramble the video and audio signals so as to decode the transmitted video and audio signals.

28. A method for scrambling and unscrambling of standard television signals as claimed in claim 24, further comprising the steps of controlling and enabling continuously the decoding step on a selective basis so that if there is no match between the control signals and the address code stored in the read-only-memory before a pre-selected time interval has elapsed the step of decoding is disabled.

29. For use with receivers in a subscription television system, a method for unscrambling of standard television signals scrambled by inversion of video signals of some horizontal scan lines on a line-by-line fashion in a pseudo-random basis to enable reception to transmitted scrambled video signals in an intelligible manner only by authorized subscribers, said method comprising the steps of:

receiving the transmitted scrambled video signals together with a plurality of unique pulse coded control signals which are transmitted separately and simultaneously during each of the horizontal scan lines to determine whether or not the video portion of the next successive horizontal scan line is to be inverted, said control signals identifying individual subscribers which are authorized to unscramble the scrambled video signals and providing information needed to unscramble the transmitted scrambled video signals;

storing a unique address code to identify a particular subscriber;

comparing each of the pulse coded control signals with the stored address code;

unscrambling of the video signals by means of decoding pulses converted from said control signals in the same sequence as used for scrambling when the step of comparing indicates a match to provide restored video signals without degradation in picture quality; and

enabling continuously the unscrambling step in response to said plurality of control signals on a selective basis so that if there is no match by the comparing step before a pre-selected time interval has elapsed the unscrambling means is automatically disabled.

30. A method for unscrambling of standard television signals as claimed in claim 29, wherein said control signals are 32-bit binary pulse trains which are utilized to identify the individual subscribers and to provide different code combinations sufficient to designate up to 2³⁰ (1,073,824) different individual subscribers.

31. A method for unscrambling of standard television signals as claimed in claim 30, wherein said storing step includes the step of providing a read-only-memory circuit to store the unique address code consisting of a 32-bit code.

32. A method for unscrambling of standard television signals as claimed in claim 31, wherein said comparing step includes the step of providing a comparator circuit to determine if any of the control signals is identical to the 32-bit code stored in the read-only-memory.

33. A method for unscrambling of standard television signals as claimed in claim 32, wherein said scrambling step further comprises the step of decoding by converting the control signals of 32-bit pulse trains into a plurality of 4-bit codes identical to scrambled pattern codes used to unscramble the video signals so as to decode the transmitted video signals.

34. A method for unscrambling of standard television signals as claimed in claim 29, further comprising the step of controlling and enabling continuously the unscrambling step on a selective basis so that if there is no match by the comparing step before a pre-selected time interval has elapsed the unscrambling means is disabled.

35. A method for unscrambling of standard television signals as claimed in claim 29, further comprising the step of requesting by telephone communication programs desired to be received.

36. A method for unscrambling of standard television signals as claimed in claim 29, further comprising means the step of receiving aural barker signals regardless of whether the subscriber is authorized to receive the unscrambled video signals so as to promote usage of the subscription televisions system.

37. A method for unscrambling of standard television signals as claimed in claim 29, further comprising the step of unscrambling audio signals received in the receiving step which included receiving scrambled audio signals consisting of coded digital audio signals.

38. For use with receivers in a subscription television system, an apparatus for unscrambling of standard television signals scrambled by inversion of standard television signals scrambled by inversion of video signals of some horizontal scan lines on a line-by-line fashion in a pseudo-random basis to enable reception of the video signals in an intelligible manner only by authorized subscribers, said apparatus comprising:

means for receiving the transmitted scrambled video signals together with a plurality of unique pulse coded control signals which are transmitted separately and simultaneously during each of the horizontal scan lines to determine whether or not the video portion of the next successive horizontal scan line is to be inverted, said control signals identifying individual subscribers which are authorized to unscramble the scrambled video signals and providing information needed to unscramble the transmitted scrambled video signals;

means for storing a unique address code to identify a particular subscriber;

means for comparing each of the pulse coded control signals with the stored address code;

means responsive to said comparing means when there is a match for unscrambling of the video and audio signals by means of decoding pulses converted from said control signals in the same sequence as used for scrambling to provide restored video signals without degradation in picture quality; and

controlling means responsive to said plurality of control signals for continuously enabling each of the individual unscrambling means at a particular subscriber receiving means on a selective basis so that if there is no comparison by the comparing means of an individual subscriber before a pre-selected time interval has elapsed the unscrambling means is automatically disabled.

39. An apparatus for unscrambling of standard television signals as claimed in claim 38, wherein said control signals are 32-bit binary pulse trains which are utilized to identify the individual subscribers and to provide different code combinations sufficient to designate up to 2⁺ (1,073,741,824) different individual subscribers.

40. An apparatus for unscrambling of standard television signals as claimed in claim 39, wherein said storing means includes a read-only-memory circuit to store the unique address code consisting of a 32-bit code.

41. An apparatus for unscrambling of standard television signals as claimed in claim 40, wherein said comparing means includes a comparator circuit to determine if any of the control signals is identical to the 32-bit code stored in the read-only-memory.

42. An apparatus for unscrambling of standard television signals as claimed in claim 41, wherein said unscrambling means include decoding means for converting the control signals of 32-bit pulse trains into a plurality of 4-bit codes identical to scrambled pattern codes used to scramble the video signals so as to decode the transmitted video signals.

43. An apparatus for unscrambling of standard television signals as claimed in claim 38, further comprising controlling means for continuously enabling the unscrambling means at a particular subscriber receiving means on a selective basis whereby if there is no comparison by the comparing means before a pre-selected time interval has lapsed the unscrambling means is disabled.

44. An apparatus for unscrambling of standard television signals as claimed in claim 38, further comprising telephone communication means for requesting programs desired to be received.

45. An apparatus for unscrambling of standard television signals as claimed in claim 38, further comprising means for receiving aural barker signals regardless of whether the subscriber is authorized to receive the unscrambled video signals so as to promote usage of the subscription television system.

46. An apparatus for unscrambling of standard television signals as claimed in claim 38, further comprising means for unscrambling audio signals received in the receiving means which included means for receiving scrambled audio signals consisting of coded digital audio signals.

48. A subscription television system as claimed in claim 39, wherein the first bits of the 32-bit binary pulse trains are always in the low state and the last bits thereof are always in the high state so as to facilitate in detection and synchronization by said receiving means.

65. In a subscription television system having means for generating and conveying composite television signals intelligible only to authorized subscribers, the television signals including a video portion, an aural portion, and an encryption codes signal comprising a sequence of encryption codes;

the aural portion comprising a periodically sampled and digitized audio signal encrypted in accordance with the encryption codes signal;

said samples occurring at least at twice the maximum audio frequency of the program audio signal;

receiver means including;

(a) encryption codes signal detector means for separating the encryption codes signal from the television signals;

(b) aural detector means for separating the digitized and encrypted audio signal from the television signals;

(c) inverse encryption means responsive to the separated encryption codes signal to return the detected audio signal to the pre-encryption digitized condition; and

(d) analog conversion means connected to the inverse encryption means to return the audio signal to the original analog format whereby program audio may be processed and presented in a conventional manner. .Iaddend. .Iadd.66. In a subscription television system having means for generating and conveying composite television signals intelligible only to authorized subscribers, the television signals including a subscriber address codes signal comprising a sequence of address codes, a video portion, and an aural portion, the aural portion comprising a periodically sampled and digitized audio signal subsequently encrypted in accordance with audio encryption codes generated from the address signal, said samples occurring at least at twice the maximum audio frequency of the program audio signal;

receiver means including;

(a) subscriber address codes signal detector means for separating the address codes signal from the television signals;

(b) aural detector means for separating the digitized and encrypted audio signal from the television signals;

(c) means for generating audio de-encryption codes responsive to the address codes signal, the de-encryption codes corresponding to the encryption codes used to initially encrypt said audio signal;

(d) inverse encryption means responsive to the de-encryption codes to return the detected audio signal to the pre-encryption digitized signal condition; and

(e) analog conversion means connected to the inverse encryption means to return the audio signal to the original analog format whereby program audio may be processed and presented in a conventional manner. .Iaddend.

66. Iadd.67. In a subscription television system, the receiver means of claim 66 comprising means responsive to the subscriber address codes signal for enabling and disabling the receiver whereby only receivers of authorized subscribers are enabled. .Iaddend. .Iadd.68. In a subscription television system, the receiver means of claim 66 comprising means responsive to a predetermined subscriber address code for enabling the receiver means for a predetermined period of time whenever said predetermined subscriber address code is detected. .Iaddend. .Iadd.69. In a subscription television system, further characterized in that the video signal is encoded in accordance with video encoding codes generated from the address codes signal;

the receiver means of claim 66 including;

(a) means for generating video decoding codes responsive to the address codes signal, the decoding codes corresponding to the encoding codes used to initially encode the video signal;

(b) inverse encoding means responsive to the decoding codes to return the video signal to the pre-encoded video format whereby program video may be processed and presented in a conventional manner. .Iaddend. .Iadd.70. In a subscription television system, the receiver means of claim 66 wherein each address code includes a plurality of binary digits, and wherein the audio de-encryption codes generating means includes binary adder means responsive to the address codes wherein the address codes binary digits are combined to produce de-encryption codes having fewer binary digits than the address codes. .Iaddend. .Iadd.71. In a subscription television system, the receiver means of claim 65 in which the inverse encryption means includes adder means wherein the de-encryption codes are subtracted from the detected audio signal to produce the pre-encrypted digitized signal. .Iaddend. .Iadd.72. A subscription television transmitter for generating television signals having a program video portion and a program aural portion in a non-standard format to enable reception of both program video and program portions in an intelligible manner only by authorized subscribers;

said television transmitter comprising;

(a) encryption code signal generating means for generating a continuous sequence of encryption codes;

(b) at least one carrier signal generator means adapted to convey the program video and program aural portions and the encryption codes signal from the transmitter to authorized subscribers;

(c) means for periodically sampling and digitizing the program audio signal, said samples occurring at least at twice the maximum audio frequency of the program audio signal;

(d) means responsive to the encryption code signal for digitally encrypting each digitized program audio sample from the digitizing means;

(e) means for combining the encryption codes signal, the digitized and encrypted audio program signal, a video program signal, with the carrier signals whereby the encryption codes signal, the digitized and encrypted audio signal and the video signal can be individually separated at a

67. receiver. .Iaddend. .Iadd.73. A subscription television transmitter for generating television signals having a program video portion and a program aural portion in a non-standard format to enable reception of both program video and program audio portions in an intelligible manner only by authorized subscribers;

said television transmitter comprising;

(a) authorized subscriber address codes signal generating means for generating a sequence of address codes;

(b) at least one carrier signal generator means adapted to convey the program video and program aural portions and the subscriber address codes signal from the transmitter to authorized subscribers;

(c) audio encryption codes generation means responsive to the subscriber address codes signal for generating a sequence of encryption codes;

(d) means for periodically sampling and digitizing the program audio signal, said samples occurring at least at twice the maximum audio frequency of the program audio signal;

(e) means responsive to the audio encryption codes for digitally encrypting each digitized program audio sample from the digitizing means;

(f) means for combining the address codes signal;

the digitized and encrypted program audio signal, a video program signal with the carrier signals whereby the address codes signal;

the digitized and encrypted program audio signal, and the program video signal may be individually separated at a receiver. .Iaddend. .Iadd.74. The subscription television transmitter of claim 73 including;

(a) video scrambler codes generation means responsive to the subscriber address codes signal;

(b) means responsive to the video scrambler codes for scrambling the program video signal whereby the subscriber address codes signal functions not only to identify authorized subscribers, but additionally, to generate

68. encrypted audio and scrambled video. .Iaddend. .Iadd.75. The subscription television transmitter of claim 73 wherein the subscriber address codes signal from the address codes generating means is comprised of successive address codes, each address code having a plurality of binary digits, and wherein the audio encryption codes generating means includes binary adder means responsive to the address codes wherein the address codes binary digits are combined to produce encryption codes having fewer binary digits than the address codes. .Iaddend. .Iadd.76. The subscription television transmitter of claim 72 in which the digitally encrypting means includes adder means wherein the audio encryption codes are added to the digitized program audio signal to produce the digitized and encrypted program audio signal. .Iaddend.