“…The simplest approach has been to apply utterance-based feature mean and variance normalization (Zhao et al, 2015;Fujita et al, 2015;Du et al, 2015;Wang et al, 2015). However, the two most effective techniques are transforming the DNN features using feature-space maximum likelihood linear regression (fMLLR) (Hori et al, 2015;Moritz et al, 2015;Vu et al, 2015;Sivasankaran et al, 2015;Tran et al, unpublished) or augmentation of the DNN features using either i-vectors, (e.g., Moritz et al, 2015;Zhuang et al, 2015), pitch-based features (Ma et al, 2015;Wang et al, 2015;Du et al, 2015) or bottleneck features (Tachioka et al, 2015), i.e., extracted from bottleneck layers in speaker classification DNNs.…”