Robert Boschgmbh

Werner Staude

Josef Sochor

Axel Schulz

A first counter operating at the PCM sampling frequency counts out the normal minimum period between successive synchronization words in the data stream. In a following 'window' the detection of another synchronization word produces a check signal and in all other cases a provisional check signal. In such other case the data for the next period are marked as dubious. A second counter counts out twice the minimum normal interval between synchronization words and in a following 'window', the appearance of a synchronization word produces a verification signal. The occurrence of a verification signal one normal interval after a provisional check signal removes the marking of intervening data as 'dubious'. If no verification signal is then produced, the intervening data are marked and treated as erroneous.

Detection and verification of lapses or shifts of synch words in PCM data

The digital signals representing successive picture points of a digital television video signal is caused to pass through, in succession, two delay circuits each providing a delay of one television line interval. This makes three places available where shift registers may be connected for stepping the digital signals at picture point intervals, so that a two-dimensional array of neighboring picture points located on adjacent portions of three television lines can be made simultaneously available for correcting the signal of the central picture point if it is found to be defective. A defective picture point is caused to be represented by a null value of digital signals by an error-correcting circuit. Thus, at the same places where the video signal shift registers are connected, gates for detecting null signals may be connected, each of which is followed by one-bit shift registers for addressing a read-only memory for controlling the choice of digital signal pairs from the picture point array which will be averaged in an averaging circuit to provide the output signal. If the digital signal of the central point of the picture point array is not defective, duplicates of this signal are provided to the averaging circuit under control of the read-only memory so that the original signal will proceed to the output of the circuit. If this signal is defective, however, the read-only memory selects a pair of signals corresponding to picture points bracketing the central point to provide the average signal, in accordance with a program that takes account of which points in the picture point array are defective. If no bracketing pair of points provides nondefective signals, the memory causes a medium gray signal to be substituted for the defective center point signal. This system has the advantage that the same stages are used and the same operating times occur in the processing of every picture point, whether the signal for that point is defective or not.

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Reinheim, Germany

Werner Staude