Improved Speaker Adaptation by Combining I-vector and fMLLR with Deep Bottleneck Networks

This paper investigates how deep bottleneck neural networks can be used to combine the benefits of both i-vectors and speaker-adaptive feature transformations. We show how a GMM-based speech recognizer can be greatly improved by applying feature-space maximum likelihood linear regression (fMLLR) transformation to outputs of a deep bottleneck neural network trained on a concatenation of regular Mel filterbank features and speaker i-vectors. The addition of the i-vectors reduces word error rate of the GMM system by 3–7% compared to an identical system without i-vectors. We also examine Deep Neural Network (DNN) systems trained on various combinations of i-vectors, fMLLR-transformed bottleneck features and other feature space transformations. The best approach results speaker-adapted DNNs which showed 15–19% relative improvement over a strong speaker-independent DNN baseline.