PULSKODMODULATION MED DYNAMISK OMRADESBEGRENSNING

1525636 Pulse-code-modulation decoding PHILIPS ELECTRONIC & AND ASSOCIATED INDUSTRIES Ltd 5 Sept 1975 [10 Sept 1974] 36620/75 Heading H3H In a pulse code modulation system with dynamic compansion the expansion in the receiver is limited to obtain a more constant loudness in the output signal. In Fig. 1, a delta modulation encoder and decoder of the type described in Specification 1,261,951 include bit-pattern recognizers 27, 28, integrators 25, 26 and multipliers 21, 22 for achieving dynamic compression. The receiver includes a limiter 29, e.g. a long-tailed pair, Fig. 2 (not shown), between the integrator 26 and multiplier 22 or between the multiplier 22 and decoding integrator 14. In a high information delta modulation system (not shown) in which step size is determined by a counter reading, the counter in the receiver may have a smaller range than the one in the transmitter to achieve the limiting. In Fig. 3, a P.C.M. encoder 47 and decoder 52 of the types described in Specification 1,170,727 are provided with dynamic compansion loops 58, 59 responsive to the frequency of occurrence of the most significant bit in the P.C.M. words, the limiter 70, e.g. a single diode or counter-connected pair of diodes, being inserted in the receiver between the multiplier 63 and Shannon decoder 52. The input to the encoder includes a differentiator 40 and a circuit 42 for adding a level voltage to the input signal.