format adaptation device 7 of the subscriber terminal tn1 fig2 or in the data formatting device 13 in the interface u1 fig4 and converted back from this into a delta modulated voice signal for this purpose the delta modulated voice signal is sampled with the pcm sampling clock and a so called pseudo pcm signal is formed in the line terminating device 3 of the subscriber terminal tn1 or in the line terminating device 11 in the interface u1 fig4 this pseudo pcm signal is handled and formatted exactly like a conventional pcm voice signal in the data format adaptation device 13 of the interface u1 fig4 or in the data format adaptation device 7 of the subscriber terminal tn1 fig2 this pseudo pcm signal is sampled with the sampling clock corresponding to the delta modulation method and the delta modulated signal is recovered as can be seen in the drawing with a time offset this delta modulated signal is then output to the second network n2 or to the subscriber line device 6 fig2 via the line terminating device 12 the same procedure conversion of the delta modulated signal into a pseudo pcm signal and the recovery of the delta modulated signal is executed in the data format adaptation device 13 of the interface u1 when the digital voice signal.