Spontaneous speech recognition using a massively parallel decoder

Since spontaneous utterances include many variations, speakerand task-independent general models do not work well. This paper proposes combining cluster-based language and acoustic models based on the framework of Massively Parallel Decoder (MPD). The MPD is a parallel decoder that has a large number of decoding units, in which each unit is assigned to each combination of element models. It runs efficiently on a parallel computer, and thus the turnaround time is comparable to conventional decoders using a single model and a processor. In the experiments conducted using lecture speeches from the Corpus of Spontaneous Japanese, two types of cluster models have been investigated: lecture-based cluster models and utterancebased cluster models. It has been confirmed that utterancebased cluster models give significantly lower recognition error rate than lecture-based cluster models in both language and acoustic modeling. It has also been shown that roughly 100 decoding units are enough in terms of recognition rate, and in the best setting, 12% reduction in word error rate was obtained in comparison with the conventional decoder.