The Effect of Spectral Space Reduction in Spontaneous Speech on Recognition Performances

Although speech derived from reading texts and similar types of speech, e.g., that from reading newspapers or that from news broadcasts, can be recognized with high accuracy, recognition performance drastically decreases for spontaneous speech. This is due to the fact that spontaneous speech and read speech are significantly different acoustically as well as linguistically. This paper analyzes differences in acoustic features between spontaneous and read speech using a large-scale spontaneous speech database "Corpus of Spontaneous Japanese (CSJ)". Using a linear transformation matrix, experimental results show that spontaneous speech can be characterized by reduced size of spectral space in comparison with that of read speech. These have also clarified that a reduction in the spectral space leads to a reduction in phoneme recognition accuracy. This result indicates that spectral reduction is one major reason for the decrease of recognition accuracy of spontaneous speech.