Abstract: An audio signal is multiplexed into a video picture signal by converting the audio signal into a sequence of digital code words from which subwords are extracted relative to a video signal line frequency. The number of bits in each subword is determined as a function of the amplitude dynamic range of the video signal, and each extracted digital subword is converted to provide analog samples with amplitudes proportional to quantizing of the corresponding digital subword. These analog samples are used to amplitude modulate an active portion of the video signal corresponding to a picture so as to provide a "composite" signal having the format of the video signal.

Abstract: The consequences of the loss of a packet are attenuated in a digital data communication apparatus using packet switching by structuring the digital data as multibit words into frames having a fixed length l and assembling the frames into packets all having the same predetermined length L=kl, where k is a predetermined integer. Continuity index words incremented by one each time a new frame or packet is assembled may be located into the frame locking word or the packet prefix. Then the number of packets which are lost may be determined at the receiver location by monitoring the successively received index words. When the digital data represent successive samples which are correlated, for instance when such samples represent a sound, substitution data may be generated at the receiver location and used in place of the missing data.