Automation of system building for state-of-the-art large vocabulary speech recognition using evolution strategy

When building a state-of-the-art speech recognition system, the laborious effort required by human experts in tuning numerous parameters remains a prominent obstacle. The goal of this paper is to automate the process. We propose to tune DNN-HMM based large vocabulary speech recognition systems using the covariance matrix adaptation evolution strategy (CMA-ES) with a multi-objective Pareto optimization. This optimizes systems to achieve both high-accuracy and compact model size. An additional advantage of our approach is that it is efficiently parallelizable and easily adapted to cloud computing services. We performed experiments on the Corpus of Spontaneous Japanese (CSJ) using the TSUBAME 2.5 supercomputer. Compared with a strong manually tuned configuration borrowed from a similar system, our approach automatically discovered systems with lower WER by 0.48%, and systems with 59% smaller model size while keeping WER constant. The optimized training script is released in the Kaldi speech recognition toolkit as the first publicly available recipe for Japanese large vocabulary speech recognition.