Method of and means for processing an audio frequency signal to conceal intelligility
US4126761A · kind A · utility
Inventors
Key dates
| Filing date | Feb 11, 1977 |
| Grant date | Nov 21, 1978 |
| Priority date | — |
| Expiry date | Feb 11, 1997 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04K1/02
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
An input audio frequency analog signal, for example, speech, which is to be passed through a noisy transmission channel, is scrambled at the sending end by repetitively performing a modulo-v (MOD v) addition of an n-level, m-pulse codeword with an n-level digitized transformation of the input signal under the condition that m and v are integers. The resultant sum signal, after transmission through a noisy channel (which may be an acoustic medium, a conventional telephone link, a conventional CB radio link, etc.), is received at the receiving end and descrambled. Descrambling is achieved by carrying out a Mod v subtraction process involving repetitively subtracting the same codeword from an n-level digitized transformation of the received signal, the subtraction being carried out in synchronism with the addition at the sending end. The resultant difference signal is a representation of the input signal and is relatively insensitive to noise present in the transmission channel.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.