Patent US 3,959,592

A method of, and apparatus for, transmitting and receiving electrical speech signals transmitted in ciphered form, wherein at the transmitter end there are formed in sections or intervals from the speech signals to be transmitted, by frequency analysis, signal components or parameter signals containing frequency spectrum-, voiced/voiceless information- and fundamental sound pitch coefficients, these signal components are ciphered, the ciphered signal components or parameter signals are transformed into a transmission signal and this transmission signal is transmitted over a transmission channel, and at the receiver end there is reobtained from the transmission signal the ciphered signal components or parameter signals and deciphered, and from the thus-obtained deciphered signal components or parameter signals there is generated by synthesis a speech signal which is similar to the original speech signal. According to the invention there is employed at the transmitter end for the synthesis of the transmission signal harmonic frequencies of a common fundamental frequency with constant fundamental period at least for each signal section or signal interval, the amplitudes of the individual harmonic frequencies are determined by means of the ciphered signal components or parameter signals, and from the received transmission signal by frequency analysis over at least a respective one full fundamental period there is reobtained the fundamental frequency of the ciphered parameter signals or signal components in intervals or sections. Further, for the receiver end synthesis of the speech which is similar to the original speech signal there are employed harmonic frequencies of a common fundamental frequency and such frequencies are individually modulated by the deciphered parameters signals or signal components, and the transmitter end-frequency analysis of the speech signal and the receiver end-frequency analysis of the transmission signal is carrier out by means of individually accessible harmonic frequencies of a respective common fundamental frequency.