Speed transformation of a data stream into a data stream with a lower bit rate

摘要

Following insertion at the transmission end of digitised additional information (additional word Z) into a data stream Dn containing n words per frame with a specific bit rate of, for example, 33.831 Mbit/s through speed transformation, a data stream D(n + 1) with a correspondingly increased bit rate of, e.g. 34.368 Mbit/s is transmitted. According to the invention, at the receiving end, in order to recover the original data stream following removal of the additional word inserted in the frame as the (n + 1)th word, for the required inverse speed transformation, a) by means of a clock T1 with a gap at this word position, the period of the nth word (n = 63) is doubled, b) the first data stream D1 thus produced is sampled in delayed fashion with a second clock T2 which is delayed in the first half of each frame by DELTA t = 1/2 pi and in the second half by DELTA t = 3/2 pi in relation to the first clock T1 so that the words in the second data stream D2 sampled at the changeover of these delay times have one and a half times the word duration: each ((n+1)/2)th word is lengthened, each nth word is shortened and c) the output data stream Dn is generated with a sampling clock T3 (T3: T1 = n : (n + 1)) synchronised to the mid-point of these excessively long words (Fig. 2). <IMAGE>