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Browse Prior Art Database

Speech Encryption Technique

IP.com Disclosure Number: IPCOM000036032D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Tubiana, M: AUTHOR

Abstract

Speech Encryption Digital Voice compression products using Voice Excited Predictive Coding (VEPC) techniques could enable securing the coded voice information at fairly low extra cost.

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Speech Encryption Technique

Speech Encryption Digital Voice compression products using Voice Excited Predictive Coding (VEPC) techniques could enable securing the coded voice information at fairly low extra cost.

The VEPC is a base-band residual excited linear prediction vocoder which provides three types of data, designated COEFF, SIGNAL and ENERG.

To that end, the original voice signal is processed on a block basis in the range of 10-40 ms. Because of the slow mechanical changes in the vocal track, for each block duration the signal can be considered to be quasi-stationary, which enables analysis. For each block of samples the analysis provides a set of 8 partial correlation (Parcor) coefficients (COEFF). This set is normally used to tune a filter for filtering the voice signal and deriving a base-band signal subsequently split into 8 sub-bands whose contents are quantized with dynamic allocations of quantizing resources. The COEFFs are used at the synthesis level to regenerate the original signal. They are therefore fundamental to the block synthesis operations.

As shown in the figure, a simple method for enciphering the voice signal could be achieved by inserting a scrambling operation over the COEFFs.

Additional flexibility could derive from enabling setting the scrambler selectively. For instance, once the link between calling and called parties is established, the parties may concurrently decide to select one among a set of predetermined scrambling functio...