单声道语音识别的逐句循环Dropout迭代说话人自适应
WRBN（wide residual BLSTM network，宽残差双向长短时记忆网络）
[2] J. Heymann, L. Drude, and R. Haeb-Umbach, "Wide residual blstm network with discriminative speaker adaptation for robust speech recognition," submitted to the CHiME, vol. 4, 2016.
reverberation，n. [声] 混响；反射；反响；回响
CLDNN（convolutional, long short-term memory, fully connected deep neural networks，卷积-长短时记忆-全连接深度神经网络）
[1] T.N. Sainath, O. Vinyals, A. Senior, and H. Sak, "Convolutional, long short-term memory, fully connected deep neural networks," in Acoustics, Speech and Signal Processing (ICASSP), 2015 IEEE International Conference on. IEEE, 2015, pp. 4580–4584.
speech separation，语音分离，将多说话人同时说话的语句分离为各个说话人独立说话的语句。
在LSTM训练中使用Dropout能有效缓解过拟合。
[3] G.E. Hinton, N. Srivastava, A. Krizhevsky, I. Sutskever, and R.R. Salakhutdinov, "Improving neural networks by preventing co-adaptation of feature detectors," arXiv preprint arXiv:1207.0580, 2012.
在输出门、遗忘门以及输入门使用基于语句采样丢帧Mask能取得最优结果（Cheng dropout）。
[7] G. Cheng, V. Peddinti, D. Povey, V. Manohar, S. Khudanpur, and Y. Yan, "An exploration of dropout with lstms," in Proceedings of Interspeech, 2017.
基于MLLR的迭代自适应方法，使用上一次迭代的解码结果来更新高斯参数。
[10] P.C. Woodland, D. Pye, and M.J.F. Gales, "Iterative unsupervised adaptation using maximum likelihood linear regression," inSpokenLanguage, 1996.ICSLP96.Proceedings., Fourth International Conference on. IEEE, 1996, vol. 2, pp. 1133–1136.
近期提出了一种batch正则化说话人自适应。
[14] P. Swietojanski, J. Li, and S. Renals, "Learning hidden unit contributions for unsupervised acoustic model adaptation," IEEE/ACMTransactionsonAudio,Speech, and Language Processing, vol. 24, no. 8, pp. 1450– 1463, 2016.
本文使用了无监督的LIN说话人自适应
[11]
使用的LIN层矩阵维数为80*80，该层被三个输入特征共享（原始、delta、delta-delta）。
本文尝试使用以下两种方式进行迭代的说话人自适应：
- 在迭代时使用上一次迭代的模型生成新标签进行训练。
- 每次迭代堆叠一个额外的线性输入层（数学上，多个线性层相当于一个隐层）
传统DNN训练方式是segment-wise
实验得出，使用RNN时，Iter（迭代方案）更优；使用tri-gram时，Stack（堆叠）方案更优