Speech privacy system

• US 3,995,115 A
• Filed: 08/25/1967
• Issued: 11/30/1976
• Est. Priority Date: 08/25/1967
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Inventors: Kelly, James M.
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US04/663,307
• Time in Patent Office: 3,385 Days
• Field of Search: 179/1.5, 179/1.5 R
• US Class Current: 380/32
• CPC Class Codes: H04K 1/04 by frequency scrambling, i.e. by transposing or inverting parts of the frequency band or by inverting the whole band

Abstract

The communication of confidential information is generally accomplished by transforming applied message waves into an unintelligible form prior to transmission. Such a transformation may be accomplished by scrambling the applied message waves in either the frequency or time domain. Scrambling, per se, does not render a signal satisfactorily unintelligible. In order to overcome this deficiency, scrambling techniques are utilized jointly with vocoder and selective speech processing methods. In a voice-excited vocoder, the spectrum channel control signals are scrambled in the frequency domain and the baseband signal is severely center clipped in order to enhance unintelligibility. A high degree of privacy during transmission is thus obtained with negligible effect upon the quality or intelligibility of speech synthesized by an authorized recipient.

Claims

1. Speech privacy transmitter apparatus comprising:

a source of speech signal,

means for developing a plurality of reduced bandwidth control signals whose instantaneous magnitudes are proportional to the instantaneous amplitudes of the components, respectively, within each of a plurality of predetermined frequency subbands of said speech signal,

means for extracting from said speech signals a signal representative of the baseband components of said speech signal,

means for rendering said plurality of reduced bandwidth control signals unintelligible prior to transmission,

means for rendering said representative baseband signal unintelligible prior to transmission,

and means for transmitting said signals which have been rendered unintelligible.

2. Speech privacy transmitter apparatus as defined in claim 1 wherein said means for rendering said plurality of reduced bandwidth control signals unintelligible comprises:

a source of a plurality of carrier wave signals,

and means for modulating said reduced bandwidth control signals with said carrier wave signals in accordance with a predetermined format.

3. Speech privacy transmitter apparatus as defined in claim 1 wherein said means for rendering said representative baseband signal unintelligible comprises:

means for amplitude clipping said baseband signal.

4. Apparatus for rendering an applied speech signal unintelligible to unauthorized personnel comprising:

vocoder means for generating from said applied speech signal a plurality of spectrum channel control signals and a baseband signal,

means for modulating in accordance with a predetermined code format said spectrum channel control signals with a plurality of carrier wave signals,

and means for center clipping said baseband signal.

5. Apparatus for rendering an applied speech signal unintelligible to unauthorized personnel comprising:

vocoder means for generating from said applied speech signal a plurality of spectrum channel control signals and a baseband signal,

means for modulating in accordance with a predetermined code format said spectrum channel control signals with a plurality of carrier wave signals,

means for center clipping said baseband signal,

and means for substituting during unvoiced and silent intervals of said speech signal noise signals for said center clipped baseband signal.

6. A speech privacy system comprising:

a source of speech signals,

vocoder analyzer means for generating from said speech signals a plurality of reduced bandwidth control signals and a representative baseband signal,

means for frequency scrambling said reduced bandwidth control signals,

means for center clipping said baseband signal,

means for replacing said center clipped baseband signal with noise signals during unvoided and silent intervals of said speech signals,

means for transmitting said frequency scrambled control signals and said center clipped baseband signal or said noise signals in replacement thereof,

means for receiving said transmitted signals,

means for unscrambling said received frequency scrambled reduced bandwidth control signals,

means for processing said received baseband signal to develop a plurality of excitation signals,

and vocoder synthesizer means responsive to said unscrambled reduced bandwidth control signals and said excitation signals for reproducing an intelligible replica of said speech signals.

7. The method of rendering a transmitted speech signal unintelligible to unauthorized personnel comprising the steps of:

generating from an applied speech signal a plurality of reduced bandwidth control signals and a baseband signal,

modulating said control signals with a plurality of carrier wave signals in accordance with a predetermined format,

and center clipping said baseband signal.