The adaptation of context-dependent deep neural network acoustic models is particularly challenging, because most of the context-dependent targets will have no occurrences in a small adaptation data set. Recently, a multi-task training technique has been proposed that trains the network with context-dependent and context-independent targets in parallel. This network structure offers a straightforward way for network adaptation by training only the context-independent part during the adaptation process. Here, we combine this simple adaptation technique with the KL-divergence regularization method also proposed recently. Employing multi-task training we attain a relative word error rate reduction of about 3 % on a broadcast news recognition task. Then, by using the combined adaptation technique we report a further error rate reduction of 2 % to 5 %, depending on the duration of the adaptation data, which ranged from 20 to 100 s.
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