We compand a one‐bit coder by increasing its step size when a string of equal bits is detected in the transmitted code. To code and decode each string we use a weight sequence 1, 1, 2, 3, 5 … 5, the weight returns to unity when the string ends. Stability considerations restrict the choice of weights but those proposed give adequate stability as well as improve the signal‐to‐noise ratio about 5 dB. The weighted coder has a wide tolerance to changes of input, so that a ±3 dB change from the design value is hardly visible to most observers. Matching weights at the transmitter and receiver is uncritical because mismatches appear as small changes of contrast rather than as noise. The circuit is easily implemented because it is tolerant to changes of component values. There is a description of an experimental coder and decoder, together with subjective and objective measures of performance. Signal‐to‐noise ratios o1 50 dB are reported.
This is a study of the visibility of television noise and its dependence on the instantaneous rate of change of the video signal. Noise added to a picture tends to be least noticeable in regions where the brightness changes rapidly, but the relationship between visibility‐of‐noise and slope‐of‐the signal is dependent on the scene being displayed. Measurements are presented for four different scenes, and these data are used to design companding laws that minimize the visibility of noise from Differential Quantizers. The designs agree with those that have been satisfactory in practical applications.
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