Method and apparatus for the secret transmission of speech signals

Abstract

Method and apparatus for enhancing the secret (confidential) transmission of voice (speech) type signals. The voice signals are encoded at a transmitter facility. Filling signals are inserted into breaks and interruptions normally encountered between words and/or phrases. Such breaks and interruptions may be either partially or completely filled with the filling signals which preferably correspond as close as is practical to the characteristic of either coded or uncoded voice signals with regard to time variation and spectral energy distribution and the filling signals may be derived from voice signals of either the coded or uncoded type which are at least temporarily stored by the transmitter facility. The resultant signal having either shortened or completely eliminated breaks and interruptions is then encoded and transmitted to a remote location. Alternatively, the voice signals may be intially encoded before the insertion of filling signals into the breaks and/or interruptions. Reversal of the operations performed at the transmitter facility takes place at the remote receiver facility in order to recover the original voice signals. A signal which controls the insertion of the filling signals may be transmitted over a separate channel for control of a responsive device at the receiver facility to provide for suppression of filling signals thereat. Various techniques and apparatus are described for achieving the above objectives.