DPCM encoder with estimated-value forming circuit

摘要

In the transmission of DPCM-coded composite PAL colour signals, the sampling frequency is generally an integral n-fold value of the PAL colour subcarrier frequency. It is known to use the samples of the pulse period of the PAL colour subcarrier frequency in each case as estimated values for the DPCM coding. If, however, composite NTSC colour signals are transmitted in a transmission system intended for composite PAl signals, the samples of the past period of the PAL colour subcarrier frequency provide unsatisfactory estimated values for the composite NTSC colour signal. Better estimated values are obtained by means of an estimated-value forming circuit in which the starting value of the estimated-value forming circuit is delayed by n+1 periods of the sampling frequency compared with the starting value of the DPCM encoder or DPCM decoder.