| 摘要 |
Process and device for protecting the transmission of vocal signals along a limited band-width analog transmission channel (for instance a vocal CCITT channel), protecting against illicite listening. By exploiting the speech information perceived by the human ear, the vocal signal to be transmitted is digitalized and undergoes a corresponding information reduction [A(f)] based on Fourier's transformation. The necessary information protection can thereby be obtained in the subsequent coding, with respect to the transmission distortions and the modulation is optimally adapted to the transmission behaviour. The digital form existing before this coding can be easily digitalized so that the transmitted analog signal is totally incomprehensible and can not be reconstituted even through the modem methods of analysis, while for the authorized listeners a good intelligibility subsists. By this process, through the modern means of the digital signal processing technique, an optimal solution to the safe analog transmission of speech can be achieved. |
