We describe the latest improvements to the IBM English conversational telephone speech recognition system. Some of the techniques that were found beneficial are: maxout networks with annealed dropout rates; networks with a very large number of outputs trained on 2000 hours of data; joint modeling of partially unfolded recurrent neural networks and convolutional nets by combining the bottleneck and output layers and retraining the resulting model; and lastly, sophisticated language model rescoring with exponential and neural network LMs. These techniques result in an 8.0% word error rate on the Switchboard part of the Hub5-2000 evaluation test set which is 23% relative better than our previous best published result.
Bibliographic reference. Saon, George / Kuo, Hong-Kwang J. / Rennie, Steven / Picheny, Michael (2015): "The IBM 2015 English conversational telephone speech recognition system", In INTERSPEECH-2015, 3140-3144.