Inter-frame dependence arising from preceding and succeeding frames – Application to speech recognition

Abstract

This paper extends the notion of capturing temporal information within an HMM framework by permitting the observed frame not only to be dependent upon preceding frames, but also upon succeeding frames. In particular the IFD–HMM (Ming and Smith, 1996) is extended to support any number of preceding and/or succeeding frame dependencies. The means through which such a dependency might be integrated into an HMM framework are explored, and details given of the resultant changes to the IFD–HMM. Experimental results are provided, contrasting the use of bi-directional frame dependencies to the use of preceding only frame dependencies and exploring how such dependencies can be best employed. It was found that a dependency upon succeeding frames enabled dynamic spectral information not found in the preceding frames to be usefully employed, resulting in a significant increase in the recognition accuracy. It was also found that the use of frame dependencies proved to be a more effective means of increasing recognition accuracy than the use of multiple mixtures.