Video transmission system

• US 4,742,543 A
• Filed: 07/10/1986
• Issued: 05/03/1988
• Est. Priority Date: 12/22/1983
• Status: Expired due to Fees

• Current Assignee: Frederiksen, Jeffrey E.
• Original Assignee: Frederiksen, Jeffrey E.
• Inventors: Frederiksen, Jeffrey E.
• Primary Examiner(s): Cangialosi, Salvatore
• Application Number:
  US06/884,217
• Time in Patent Office: 663 Days
• Field of Search: 179/1.5 R, 179/1.5 M, 358/119, 358/121, 358/145, 358/147, 380/9, 380/10, 380/19, 380/46, 380/33, 380/49, 375/26, 381/31
• US Class Current: 380/237
• CPC Class Codes: H04N 7/085 the inserted signal being digital
• CPC Class Codes: H04N 7/1696 by changing or reversing the order of active picture signal portions

Abstract

A subscriber cable television system uses predominantly digital signal processing techniques and has extremely high security and an increased capacity for transmitting program and customer data to individual decoder units. For ease of data handling, two-channel audio, video, and high capacity program and customer data are multiplexed for transmission on the composite video signal. The decoder unit employs a system timing circuit which precisely synchronizes the sample times on the received composite video signal to the chroma burst, regardless of whether the video information is for a color or black-and-white program. An improved time-warp and segment scrambling method is disclosed along with means for suppressing the undesirable effects of discontinuities in the scrambled video signal. The digital audio is transmitted as scrambled most significant bits in low resolution samples and unscrambled least significant bits in a high resolution remainder sample. The system timing circuit has a horizontal sync detector accommodating variable line length such as is provided by some video recording apparatus. The clock to the horizontal counter is selectively phase-reversed in response to early or late horizontal sync so that the timing resolution is twice the clock period. An improved self-adjusting threshold detector and other means are disclosed for detecting a "20 IEEE" suppressed horizontal sync so that the full range of video modulation may be used more effectively. Circuitry is also disclosed for transmitting the customer and program information in a multi-level correlative signalling format in order to more effectively use the band width of the entire television channel.

Claims

1. A method of transmitting an audio signal comprising the steps of:

(a) repetitively digitizing the audio signal to repetitively generate a digital portion and a respective remainder portion, wherein said digitizing is performed by sampling the audio signal at spaced instants in time and quantizing each audio sample to a certain number of spaced levels, the digital portion being the quantized audio sample, the remainder portion being approximately the difference between the audio signal and the digital portion at said spaced instants in time,

(b) transmitting the digital portions and their respective remainder portions as a series of analog samples, the analog samples representing the digital portions being quantized to more than two levels, the analog samples representing the remainder portions having substantially more resolution than the resolution of the analog samples representing the digital portions, each remainder portion being transmitted as a single analog sample,

(c) receiving the series of analog samples, quantizing the analog samples representing digital portions to generate quantized values, and adding the quantized values to values of the respective analog samples representing remainder portions to thereby generate a series of values representing the transmitted audio signal.

2. The method as claimed in claim 1, wherein the digital portions are scrambled by pseudorandom numbers before transmission, and wherein the digital portions are descrambled by the same pseudo-random numbers after transmission.

3. A method of transmitting an audio signal comprising the steps of:

(a) repetitively digitizing the audio signal to repetitively generate a digital portion and a remainder portion, the remainder portion being approximately the difference between the audio signal and the digital portion at spaced instants in time,

(b) transmitting the digital portions and their respective remainder portions as a series of analog samples, the analog samples representing the digital portions being quantized to more than two levels, the analog samples representing the remainder portions having substantially more resolution than the resolution of the analog samples representing the digital portions, each remainder portion being transmitted as a single analog sample,

(c) receiving the series of analog samples, quantizing the analog samples representing digital portions to generate quantized values, and adding the quantized values to values of the respective analog samples representing remainder portions to threreby generate a series of values representing the transmitted audio signal, wherein the step of digitizing includes digitizing the audio signal to 12 bit resolution at said spaced instants in time, each digital portion including the four most significant bits and each remainder portion including the eight least significant bits.

4. The method as claimed in claim 3, wherein each digital portion is transmitted as two analog samples, each analog sample being quantized to four levels, and wherein each remainder portion is transmitted as a single analog sample.

5. The method as claimed in claim 3, wherein the digital portions are scrambled by pseudo-random numbers before transmission, and wherein the digital portions are descrambled by the same pseudo-random numbers after transmission.

6. A method of transmitting an audio signal in a composite video signal comprising the steps of:

(a) repetitively digitizing the audio signal to repetititively generate a digital portion and a respective remainder portion, wherein said digitizing is performed by sampling the audio signal at spaced instants in time and quantizing each audio sample to at least sixteen spaced levels to generate the digital portion, the digital portion being the audio sample quantized to four bits of resolution, the respective remainder portion having a value that is approximately the difference between the audio sample and the respective digital portion at the respective spaced instants in time,

(b) transmitting the digital portions and their respective remainder portions as a series of analog samples interlaced with a video signal in said composite video signal, the analog samples representing the remainder portions having substantially more resolution than the resolution of the analog samples representing the digital portions, wherein each digital portion is transmitted as two analog samples each of which is quantized to four levels, and wherein each remainder portion is transmitted as a single analog sample,

(c) receiving the series of analog samples, quantizing the analog samples representing the digital portions to generate quantized values, and adding the quantized values to values of the analog samples representing the respective remainder portions to thereby generate a series of values representing the transmitted audio signal.

7. The method as claimed in claim 6, wherein the digital portions are scrambled by pseudo-random numbers before transmission, and wherein the digital portions are descrambled by the same pseudo-random numbers after transmission.