A Companded One-Bit Coder for Television Transmission

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 of 50 dB are reported.