| 摘要 |
PURPOSE:To transmit the pseudo random series signal from transmission side to reception side in cryptogram, limitting the band of said signal by the given band pass filter, to constitute it into noise shape masking signal having an envelope to similar that of the audio signal and synthesizing it with the audio signal. CONSTITUTION:The audio signal fed to an input terminal 1 is added to an adder 11 and after it is added and synthesized with the masking signal from a masking signal generating circuit 12, it is made into a cryptogram at a cryptogram circuit 13 and delivered to a transmission circuit 3 from an output terminal 2. In general, M series virtual random signal is produced in the clock of frequency fC and it is through the narrow band filter having the pass band of, for example, fC/5 or less, then noise shape signal having Gauss distribution in the amplitude can principally be obtained. By suitably selecting the characteristics of the band pass filter 123, the frequency component and the envelope change are similar to those of audio signal, and this is used as the masking signal. |
