a method and apparatus are disclosed for scrambling and descrambling an audio signal . an interference signal is generated and is intermittently , preferably pseudo - randomly , added to the program audio as a function of control information generated either by means of hardware alone or by means of software . the scrambled audio and the interference signal are preferably transmitted on two carriers , e . g ., two standard subcarriers used in tv broadcasting , together with the control information . a decoder descrambles the audio by substracting the interference signal from the scrambled audio at the proper times as indicated by the control information . preferably , the interference signal , comprising a series of noise bursts , is transmitted on the same carrier as the control information , time - multiplexed with the latter . alternatively , the program audio itself , subjected to a time delay , is used as the interference signal , in which case the second carrier bears only the control information .