Yoshihiko Akaiwa

Voice scrambler using frequency‐inversion and band‐splitting technique

A spectrum inversion type voice scrambler for secret speech communication comprises a first spectrum inversion section, a second inversion section and an adder for summing the outputs of the first and second inversion sections. A random signal generator produces two random signals for controlling, respectively, the spectrum inversion in the two inversion sections. The first inversion section is comprised of a modulator section composed of a variable frequency signal generator response to a random signal, a mixer receiving an input signal and the output of the variable frequency generator. The second inversion section includes three modulator sections the first and third of which are composed of a fixed frequency generator, a mixer and a low pass filter. The second modulator section is composed of a variable frequency generator responsive to the second random signal, a mixer and a low pass filter. The first modulator receives the input signal, while the third modulator has its output connected to the adder which also receives the output of the first spectrum inversion section. By the above arrangement only one type of filter, a low pass filter, is needed.