An experimental system for acoustic-phonetic decoding of continuous speech

In the framework of MYRTILLE II Speech Understanding System under development in our Laboratory we have realized a prototype for the acoustic-phonetic processing level. This prototype makes it possible to test various parameters and strategies for phonemic transcription of continuous speech. It can be considered as a metasystem in the sense that, given a hierarchy of recognition algorithms and a strategy, it can generate the optimal system for phoneme recognition. The system directly works on the digitized speech wave, which makes it possible to get the best accuracy on the parameters. The speech signal is segmented into phoneme-like units by a decision function which incorporates voicing, energy, zero-crossing rate and curve length. The segments thus obtained are then processed by the recognition system which can be viewed as a tree structure the nodes of which are algorithms. These algorithms take into account one or several features and their answers can be phoneme classes and/or other algorithms. Problems involved in the design of such a system are also presented in this paper together with a particular implementation.