Design and use of speech recognition algorithms for a mobile radio telephone

To decrease the hazards of using mobile phones while driving, voice processing provides several tools that simplify their use: echo cancellation allows comfortable hands-free conversation, feedback and user guidance by voice allow to operate the phone in eyes-busy situations, and last not least speech recognition frees from keypad data entry to operate the telephone. A comprehensive view of a device incorporating the above mentioned technologies, which has been realized as an add-on for the Philips car telephone family, will be presented. Emphasis is placed on the speech recognition algorithms. Robustness of the algorithms to changing acoustic environment was improved by estimating and subtracting the long-term spectrum. We will show that, if this operation is done recursively, it is equivalent to the high-pass filtering or RASTA (Relative Spectral Approaches) methods recently proposed in the literature.