EMBEDDED SIGNALLING

Dans ce système de signalisation intégrée on produit une séquence de symboles de codage représentant une information numérique (100). On produit également un signal de codage représentant cette séquence (200), qui subit un filtrage dynamique pour constituer un signal de codage modifié (300), lequel est combiné (400) à un signal audio de niveau supérieur pour former un signal audio composite destiné à être diffusé. A code signal representing a sequence of code symbols carrying digital information is generated with the frequency components of the code signal being essentially confined to a preselected signalling band lying within the bandwidth of an audio signal within which the code signal is to be embedded. The audio signal is continuously frequency analyzed over a frequency band encompassing the signalling band and the code signal is dynamically filtered as a function of the analysis thereby to provide a modified code signal with frequency components which are, at each time instant, essentially a preselected small proportion of the levels of the corresponding audio signal frequency components. Accordingly, the modified code signal can be combined with the audio signal to obtain a composite audio signal which is not readily distinguishable from the original audio signal by listening. Furthermore, the digital information can be recovered from the composite audio signal by a procedure which is essentially the compliment of that used to obtain the composite audio signal.